Sessions: edit form, soft-delete, lazy creation, chat as separate page

- Session click opens edit form (name, description, image, agent) instead of chat
- Chat is now a separate route (#chat/{id}), opened via button
- Sessions created on save, not on click
- Soft-delete for sessions (is_deleted flag)
- Delete button in session form
- Removed title double-click editing from chat
- Card images now square (aspect-ratio: 1)
- New Session as placeholder card

wwwroot/index.html

@@ -27,7 +27,6 @@
     <section>
       <div class="section-header">
         <h2>Sessions</h2>
-        <button id="newSessionBtn">+ Neue Session</button>
       </div>
       <div class="card-grid" id="sessionCards"></div>
     </section>
@@ -48,11 +47,39 @@
 </template>
 
 <template id="tpl-session">
-  <div class="page session-page">
+  <div class="page session-edit-page">
     <header class="session-header">
       <button class="back-btn" data-page="dashboard">←</button>
-      <h1 id="sessionTitle" class="editable-title">Session</h1>
+      <h1 id="sessionPageTitle">Session</h1>
+      <button id="openChatBtn" hidden>Chat öffnen</button>
+    </header>
+    <div class="agent-form">
+      <div class="agent-avatar-section">
+        <div class="agent-avatar-preview" id="sessionImagePreview">?</div>
+        <input type="file" id="sessionImageInput" accept="image/*" hidden>
+        <button id="sessionImageBtn">Bild ändern</button>
+        <button id="sessionImageClearBtn">Entfernen</button>
+      </div>
+      <label>Name</label>
+      <input type="text" id="sessionName" placeholder="Name der Session">
+      <label>Beschreibung</label>
+      <textarea id="sessionDescription" rows="3" placeholder="Beschreibung (optional)"></textarea>
+      <label>Agent</label>
       <select id="agentSelect"></select>
+      <div class="agent-form-actions">
+        <button id="sessionSaveBtn">Speichern</button>
+        <button id="sessionCancelBtn">Abbrechen</button>
+        <button id="sessionDeleteBtn" class="danger-btn" hidden>Löschen</button>
+      </div>
+    </div>
+  </div>
+</template>
+
+<template id="tpl-chat">
+  <div class="page session-page">
+    <header class="session-header">
+      <button class="back-btn" id="chatBackBtn">←</button>
+      <h1 id="sessionTitle">Session</h1>
       <button class="header-btn" id="archiveBtn">Archivieren</button>
       <div class="toggle">
         <input type="checkbox" id="showSystem">
@@ -127,6 +154,7 @@
 <script src="js/pages/dashboard.js"></script>
 <script src="js/pages/agent-page.js"></script>
 <script src="js/pages/session-page.js"></script>
+<script src="js/pages/chat-page.js"></script>
 <script src="js/app.js"></script>
 </body>
 </html>