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/daemon/routing.ts

@@ -58,9 +58,18 @@ export function createMessageRouter(deps: {
     if (!entry) {
       const session = deps.sessionManager.getSession(channel, senderId);
 
+      // Read per-session model tier override (persisted in SQLite)
+      const sessionTierOverride = session.getConfig('modelTier') as ModelTier | undefined;
+
+      // Resolution chain: metadata (cron) → session override → agent config → global default
+      const effectiveTier = tierFromMetadata
+        ?? sessionTierOverride
+        ?? agentConfig?.modelTier
+        ?? deps.config.agents.primary_tier
+        ?? 'default';
+
       // Use agent config overrides where available, falling back to global config
       const effectiveSystemPrompt = agentConfig?.systemPrompt ?? deps.systemPrompt;
-      const effectiveTier = tierFromMetadata ?? agentConfig?.modelTier ?? deps.config.agents.primary_tier ?? 'default';
       const effectiveProvider = deps.config.models.default.provider;
 
       const delegationConfig: DelegationConfig = {
@@ -166,6 +175,46 @@ export function createMessageRouter(deps: {
     if (msg.metadata?.isCommand) {
       if (msg.metadata.command === 'reset') {
         agent.reset();
+        // Clear per-session config overrides
+        const session = deps.sessionManager.getSession(msg.channel, msg.senderId);
+        session.deleteConfig('modelTier');
+        return;
+      }
+      if (msg.metadata.command === 'model') {
+        const modelArg = msg.metadata.commandArgs as string | undefined;
+        const session = deps.sessionManager.getSession(msg.channel, msg.senderId);
+
+        if (!modelArg) {
+          // Show current model tier
+          const currentTier = agent.getModelTier();
+          const sessionOverride = session.getConfig('modelTier');
+          const available = deps.modelRouter.getAvailableTiers();
+          const labels = deps.modelRouter.getAllLabels();
+          const lines = [`Active tier: ${currentTier}${sessionOverride ? ' (session override)' : ''}`];
+          for (const tier of available) {
+            const label = labels[tier] ?? 'unknown';
+            const marker = tier === currentTier ? ' ←' : '';
+            lines.push(`  ${tier}: ${label}${marker}`);
+          }
+          await reply({ text: lines.join('\n'), replyTo: msg.id });
+          return;
+        }
+
+        // Validate tier
+        const validTiers = deps.modelRouter.getAvailableTiers();
+        if (!validTiers.includes(modelArg as ModelTier)) {
+          await reply({ text: `Model tier not available: ${modelArg}`, replyTo: msg.id });
+          return;
+        }
+
+        // Persist to session config
+        session.setConfig('modelTier', modelArg);
+
+        // Update the orchestrator's agent tier
+        agent.setModelTier(modelArg as ModelTier);
+
+        const label = deps.modelRouter.getLabel(modelArg as ModelTier);
+        await reply({ text: `Switched to model: ${modelArg} (${label})`, replyTo: msg.id });
         return;
       }
       if (msg.metadata.command === 'compact') {
@@ -215,8 +264,13 @@ export function createMessageRouter(deps: {
     try {
       // Determine if the active model supports native audio input
       let effectiveTier: string = deps.config.agents.primary_tier ?? 'default';
+      const session = deps.sessionManager.getSession(msg.channel, msg.senderId);
+      const sessionTierOverride = session.getConfig('modelTier');
+
       if (msg.metadata?.modelTier) {
         effectiveTier = msg.metadata.modelTier as string;
+      } else if (sessionTierOverride) {
+        effectiveTier = sessionTierOverride;
       } else if (deps.agentRouter && deps.agentConfigRegistry) {
         const agentName = deps.agentRouter.resolve(msg.channel, msg.senderId);
         if (agentName) {