feat(P4-003): @mosaic/log — log ingest, parsing, tiered storage

Implement AgentLogsRepo with structured log ingest (single + batch),
flexible query builder (filter by session, level, category, tier,
date range), and tiered storage management (hot→warm→cold→purge).
Add getLogsForSummarization() for the summarization pipeline.
Wire LogModule into gateway with REST endpoints at /api/logs.

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

packages/log/package.json

@@ -1,6 +1,7 @@
 {
   "name": "@mosaic/log",
   "version": "0.0.0",
+  "type": "module",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
   "exports": {
@@ -15,6 +16,10 @@
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests"
   },
+  "dependencies": {
+    "@mosaic/db": "workspace:*",
+    "drizzle-orm": "^0.45.1"
+  },
   "devDependencies": {
     "typescript": "^5.8.0",
     "vitest": "^2.0.0"