Agents: CRUD, DB table, session binding, replace model picker

- agents table with name, avatar, description, model, persona, instructions, soft-delete
- AgentEndpoint (GET/POST/PUT/DELETE /api/agents)
- sessions + chains now reference agent_id
- ChatEndpoint resolves agent from session (no agent = no chat)
- system prompt built from agent persona + instructions
- frontend: agent editor with avatar upload, agent cards on dashboard
- session: agent dropdown replaces model picker, choice persisted

wwwroot/js/pages/agent-page.js

@@ -0,0 +1,98 @@
+// ── Agent Page ──
+
+let _agentAvatarData = null;
+
+registerPage('agent', {
+  async init(params) {
+    const agentId = params.id;
+    const isNew = !agentId;
+    let agent = null;
+
+    if (!isNew) {
+      agent = await apiGetAgent(agentId);
+      if (!agent) return navigateTo('dashboard');
+    }
+
+    const title = document.getElementById('agentPageTitle');
+    const nameEl = document.getElementById('agentName');
+    const descEl = document.getElementById('agentDescription');
+    const modelEl = document.getElementById('agentModel');
+    const personaEl = document.getElementById('agentPersona');
+    const instructionsEl = document.getElementById('agentInstructions');
+    const avatarPreview = document.getElementById('avatarPreview');
+    const avatarInput = document.getElementById('avatarInput');
+    const avatarBtn = document.getElementById('avatarBtn');
+    const avatarClearBtn = document.getElementById('avatarClearBtn');
+    const saveBtn = document.getElementById('agentSaveBtn');
+    const cancelBtn = document.getElementById('agentCancelBtn');
+    const deleteBtn = document.getElementById('agentDeleteBtn');
+
+    _agentAvatarData = null;
+
+    if (agent) {
+      title.textContent = agent.name;
+      nameEl.value = agent.name || '';
+      descEl.value = agent.description || '';
+      modelEl.value = agent.model || 'sonnet';
+      personaEl.value = agent.persona || '';
+      instructionsEl.value = agent.instructions || '';
+      _agentAvatarData = agent.avatar || null;
+      deleteBtn.hidden = false;
+
+      if (agent.avatar) {
+        avatarPreview.innerHTML = `<img src="${agent.avatar}" alt="Avatar">`;
+      }
+    }
+
+    // Avatar Upload
+    avatarBtn.addEventListener('click', () => avatarInput.click());
+    avatarInput.addEventListener('change', () => {
+      const file = avatarInput.files[0];
+      if (!file) return;
+      const reader = new FileReader();
+      reader.onload = () => {
+        _agentAvatarData = reader.result;
+        avatarPreview.innerHTML = `<img src="${reader.result}" alt="Avatar">`;
+      };
+      reader.readAsDataURL(file);
+    });
+
+    avatarClearBtn.addEventListener('click', () => {
+      _agentAvatarData = null;
+      avatarPreview.innerHTML = '?';
+      avatarInput.value = '';
+    });
+
+    // Speichern
+    saveBtn.addEventListener('click', async () => {
+      const data = {
+        name: nameEl.value.trim() || 'Unbenannt',
+        description: descEl.value.trim(),
+        model: modelEl.value,
+        persona: personaEl.value,
+        instructions: instructionsEl.value,
+        avatar: _agentAvatarData
+      };
+
+      if (isNew) {
+        await apiCreateAgent(data);
+      } else {
+        await apiUpdateAgent(agentId, data);
+      }
+      navigateTo('dashboard');
+    });
+
+    // Abbrechen
+    cancelBtn.addEventListener('click', () => navigateTo('dashboard'));
+
+    // Löschen
+    deleteBtn.addEventListener('click', async () => {
+      if (!confirm('Agent wirklich löschen?')) return;
+      await apiDeleteAgent(agentId);
+      navigateTo('dashboard');
+    });
+  },
+  destroy() {
+    _agentAvatarData = null;
+  }
+});

wwwroot/js/pages/dashboard.js

@@ -2,6 +2,7 @@
 
 registerPage('dashboard', {
   async init() {
+    // Sessions laden
     const sessions = await apiGetSessions();
     const grid = document.getElementById('sessionCards');
     grid.innerHTML = '';
@@ -19,14 +20,42 @@ registerPage('dashboard', {
       grid.appendChild(card);
     }
 
-    // Neue Session Button
-    const btn = document.getElementById('newSessionBtn');
-    if (btn) {
-      btn.addEventListener('click', async () => {
+    const newSessionBtn = document.getElementById('newSessionBtn');
+    if (newSessionBtn) {
+      newSessionBtn.addEventListener('click', async () => {
         const session = await apiCreateSession();
         navigateTo('session', { id: session.sessionId });
       });
     }
+
+    // Agents laden
+    const agents = await apiGetAgents();
+    const agentGrid = document.getElementById('agentCards');
+    agentGrid.innerHTML = '';
+
+    for (const a of agents) {
+      const card = document.createElement('div');
+      card.className = 'card clickable';
+      card.innerHTML = `
+        <div class="agent-card-avatar">${a.avatar ? `<img src="${a.avatar}" alt="">` : '?'}</div>
+        <div class="card-title">${escHtml(a.name)}</div>
+        <div class="card-sub">${escHtml(a.model || 'sonnet')}</div>
+      `;
+      card.addEventListener('click', () => {
+        navigateTo('agent', { id: a.agentId });
+      });
+      agentGrid.appendChild(card);
+    }
+
+    // Neuer Agent Placeholder
+    const placeholder = document.createElement('div');
+    placeholder.className = 'card placeholder clickable';
+    placeholder.innerHTML = `
+      <div class="card-icon">+</div>
+      <div class="card-title">Neuer Agent</div>
+    `;
+    placeholder.addEventListener('click', () => navigateTo('agent'));
+    agentGrid.appendChild(placeholder);
   },
   destroy() {}
 });

wwwroot/js/pages/session-page.js

@@ -1,7 +1,5 @@
 // ── Session Page ──
 
-let _sessionPageCleanup = [];
-
 registerPage('session', {
   async init(params) {
     const sessionId = params.id;
@@ -9,7 +7,7 @@ registerPage('session', {
 
     currentSessionId = sessionId;
 
-    // Session-Name laden
+    // Session laden
     const session = await apiGetSession(sessionId);
     const titleEl = document.getElementById('sessionTitle');
     if (session && titleEl) {
@@ -17,6 +15,42 @@ registerPage('session', {
       titleEl.addEventListener('dblclick', () => editTitle(sessionId, titleEl));
     }
 
+    // Agent-Auswahl laden
+    const agentSelect = document.getElementById('agentSelect');
+    const sendBtn = document.getElementById('send');
+    const inputEl = document.getElementById('input');
+
+    if (agentSelect) {
+      const agents = await apiGetAgents();
+      agentSelect.innerHTML = '<option value="">-- Agent wählen --</option>';
+      for (const a of agents) {
+        const opt = document.createElement('option');
+        opt.value = a.agentId;
+        opt.textContent = `${a.name} (${a.model})`;
+        agentSelect.appendChild(opt);
+      }
+
+      // Gespeicherten Agent setzen
+      if (session && session.agentId) {
+        agentSelect.value = session.agentId;
+      }
+
+      // Agent-Wechsel speichern
+      agentSelect.addEventListener('change', async () => {
+        const val = agentSelect.value || null;
+        await apiUpdateSession(sessionId, { agentId: val });
+        updateSendState();
+      });
+    }
+
+    // Send-Button State
+    function updateSendState() {
+      const hasAgent = agentSelect && agentSelect.value;
+      if (sendBtn) sendBtn.disabled = !hasAgent;
+      if (inputEl) inputEl.disabled = !hasAgent;
+    }
+    updateSendState();
+
     // System Prompt Toggle
     const showSystem = document.getElementById('showSystem');
     const systemPrompt = document.getElementById('systemPrompt');
@@ -27,18 +61,13 @@ registerPage('session', {
     }
 
     // Send
-    const sendBtn = document.getElementById('send');
     if (sendBtn) sendBtn.addEventListener('click', sendMessage);
 
     // Ctrl+Enter
-    const inputEl = document.getElementById('input');
     if (inputEl) {
-      const keyHandler = (e) => {
+      inputEl.addEventListener('keydown', (e) => {
         if (e.ctrlKey && e.key === 'Enter') sendMessage();
-      };
-      inputEl.addEventListener('keydown', keyHandler);
-
-      // Auto-Resize
+      });
       inputEl.addEventListener('input', function () {
         this.style.height = 'auto';
         this.style.height = Math.min(this.scrollHeight, 150) + 'px';