feat: Avatar Position-Offset (translate X/Y)

Backend:
- AgentRecord + SessionRecord: AvatarOffsetX, AvatarOffsetY Properties
- DB-Migration: avatar_offset_x/y REAL DEFAULT 0 auf agents + sessions
- Agent/Session Endpoints: Create + Update lesen/schreiben Offset-Felder
- GetSessionsWithStats: Offset-Felder ans Frontend

Frontend:
- Avatar-Editor: X/Y Offset-Slider (-50% bis +50%) im Modal
  - buildTransformStyle() Helper für transform: scale() translate()
  - getOffsetX()/getOffsetY() Public API
  - Reset bei Clear/AI-Generate/Upload
- ui.js: buildAgentCard + buildSessionCard rendern transform mit Offset
- Agent-Page + Session-Page: initialOffsetX/Y + Save
- CSS: .av-offset-row Styles (gruppiert mit .av-scale-row)

wwwroot/js/pages/agent-page.js

@@ -38,7 +38,9 @@ registerPage('agent', {
     _agentAvatarEditor = AvatarEditor.init({
       previewEl: avatarPreview,
       initialImage: (agent && agent.avatar) || null,
-      initialScale: (agent && agent.avatarScale) || 1
+      initialScale: (agent && agent.avatarScale) || 1,
+      initialOffsetX: (agent && agent.avatarOffsetX) || 0,
+      initialOffsetY: (agent && agent.avatarOffsetY) || 0
     });
 
     if (agent) {
@@ -100,6 +102,8 @@ registerPage('agent', {
         webSearchVersion: webSearchVersionEl.value,
         avatar: _agentAvatarEditor.getImage(),
         avatarScale: _agentAvatarEditor.getScale(),
+        avatarOffsetX: _agentAvatarEditor.getOffsetX(),
+        avatarOffsetY: _agentAvatarEditor.getOffsetY(),
         customCommands: getCommandsFromUI(commandsList)
       };
 

wwwroot/js/pages/session-page.js

@@ -37,7 +37,9 @@ registerPage('session', {
     _sessionAvatarEditor = AvatarEditor.init({
       previewEl: imagePreview,
       initialImage: (session && session.image) || null,
-      initialScale: (session && session.avatarScale) || 1
+      initialScale: (session && session.avatarScale) || 1,
+      initialOffsetX: (session && session.avatarOffsetX) || 0,
+      initialOffsetY: (session && session.avatarOffsetY) || 0
     });
 
     if (session) {
@@ -190,7 +192,9 @@ registerPage('session', {
         context: _sessionContextMde.value().trim() || null,
         workspace: workspaceEl.value.trim() || null,
         customCommands: commands,
-        avatarScale: _sessionAvatarEditor.getScale()
+        avatarScale: _sessionAvatarEditor.getScale(),
+        avatarOffsetX: _sessionAvatarEditor.getOffsetX(),
+        avatarOffsetY: _sessionAvatarEditor.getOffsetY()
       };
 
       if (isNew) {