feat: implement model persistence with per-session overrides

- Add session_config SQLite table for per-session settings
- Update routing to support session override → agent config → global default resolution chain
- Upgrade WebChat SessionBridge from NativeAgent to AgentOrchestrator
- Add /model, /local, /cloud commands to Telegram adapter
- Add /model command to WebChat gateway handlers
- Clear session overrides on /reset command
- Pass memoryStore and config through to SessionBridge
- Add comprehensive tests for all new functionality

Fixes model persistence bug where TUI model changes didn't affect WebChat/Telegram sessions. Now:
- TUI /model sets global default (persists across restarts, affects all new sessions)
- WebChat/Telegram /model sets session override (only that conversation, cleared on /reset)
- WebChat sessions gain AgentOrchestrator features (delegation, compaction, memory)

src/channels/telegram/adapter.test.ts

@@ -62,10 +62,13 @@ describe('TelegramAdapter', () => {
 
     // .use() for auth middleware
     expect(mockUse).toHaveBeenCalledTimes(1);
-    // .command() for /start and /reset
-    expect(mockCommand).toHaveBeenCalledTimes(2);
+    // .command() for /start, /reset, /model, /local, /cloud
+    expect(mockCommand).toHaveBeenCalledTimes(5);
     expect(mockCommand.mock.calls[0][0]).toBe('start');
     expect(mockCommand.mock.calls[1][0]).toBe('reset');
+    expect(mockCommand.mock.calls[2][0]).toBe('model');
+    expect(mockCommand.mock.calls[3][0]).toBe('local');
+    expect(mockCommand.mock.calls[4][0]).toBe('cloud');
     // .on('message:text', ...) for text handler
     expect(mockOn).toHaveBeenCalledWith('message:text', expect.any(Function));
     // .start() to begin long polling

src/channels/telegram/adapter.ts

@@ -163,6 +163,52 @@ export class TelegramAdapter implements ChannelAdapter {
       await ctx.reply('Conversation reset.');
     });
 
+    this.bot.command('model', async (ctx) => {
+      if (!this.messageHandler) return;
+
+      const args = ctx.message?.text?.replace(/^\/model\s*/, '').trim() ?? '';
+
+      this.messageHandler({
+        id: String(ctx.message?.message_id ?? Date.now()),
+        channel: 'telegram',
+        senderId: String(ctx.chat.id),
+        senderName: ctx.from?.first_name,
+        text: `/model ${args}`.trim(),
+        timestamp: Date.now(),
+        metadata: {
+          isCommand: true,
+          command: 'model',
+          commandArgs: args || undefined,
+        },
+      });
+    });
+
+    this.bot.command('local', async (ctx) => {
+      if (!this.messageHandler) return;
+      this.messageHandler({
+        id: String(ctx.message?.message_id ?? Date.now()),
+        channel: 'telegram',
+        senderId: String(ctx.chat.id),
+        senderName: ctx.from?.first_name,
+        text: '/model local',
+        timestamp: Date.now(),
+        metadata: { isCommand: true, command: 'model', commandArgs: 'local' },
+      });
+    });
+
+    this.bot.command('cloud', async (ctx) => {
+      if (!this.messageHandler) return;
+      this.messageHandler({
+        id: String(ctx.message?.message_id ?? Date.now()),
+        channel: 'telegram',
+        senderId: String(ctx.chat.id),
+        senderName: ctx.from?.first_name,
+        text: '/model default',
+        timestamp: Date.now(),
+        metadata: { isCommand: true, command: 'model', commandArgs: 'default' },
+      });
+    });
+
     // ── Text message handler ──
 
     this.bot.on('message:text', async (ctx) => {