feat(P4-001): @mosaic/memory — preference + insight stores

Add memory tables to DB schema (preferences, insights with pgvector
embedding column, agent_logs, skills, summarization_jobs). Implement
PreferencesRepo (CRUD + upsert) and InsightsRepo (CRUD + semantic
search + relevance decay). Define VectorStore and EmbeddingProvider
interfaces for future provider abstraction. Wire MemoryModule into
gateway with REST endpoints at /api/memory/*.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/memory/package.json

@@ -1,6 +1,7 @@
 {
   "name": "@mosaic/memory",
   "version": "0.0.0",
+  "type": "module",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
   "exports": {
@@ -16,7 +17,9 @@
     "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
-    "@mosaic/types": "workspace:*"
+    "@mosaic/db": "workspace:*",
+    "@mosaic/types": "workspace:*",
+    "drizzle-orm": "^0.45.1"
   },
   "devDependencies": {
     "typescript": "^5.8.0",