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>

pnpm-lock.yaml

@@ -59,6 +59,9 @@ importers:
       '@mosaic/db':
         specifier: workspace:^
         version: link:../../packages/db
+      '@mosaic/log':
+        specifier: workspace:^
+        version: link:../../packages/log
       '@mosaic/memory':
         specifier: workspace:^
         version: link:../../packages/memory
@@ -324,6 +327,13 @@ importers:
         version: 2.1.9(@types/node@22.19.15)(lightningcss@1.31.1)
 
   packages/log:
+    dependencies:
+      '@mosaic/db':
+        specifier: workspace:*
+        version: link:../db
+      drizzle-orm:
+        specifier: ^0.45.1
+        version: 0.45.1(@opentelemetry/api@1.9.0)(@types/pg@8.15.6)(kysely@0.28.11)(postgres@3.4.8)
     devDependencies:
       typescript:
         specifier: ^5.8.0