feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/tools/builtin/memory-read.ts

@@ -13,7 +13,7 @@ export function createMemoryReadTool(store: MemoryStore): Tool {
   return {
     name: 'memory.read',
     description:
-      'Read a persistent memory file by namespace. Available namespaces include "user" (user preferences and facts), "global" (cross-session knowledge), and session-specific namespaces. Returns the full contents of the memory file.',
+      'Read a persistent memory file by namespace. Available namespaces include "user" (user preferences and facts), "global" (cross-session knowledge), and session-specific namespaces. Supports structured categories by appending /facts, /preferences, /decisions, or /projects (for example: "user/facts"). Returns the full contents of the memory file.',
     inputSchema: {
       type: 'object',
       properties: {