feat(db): Postgres schema, migrations and defects repository (T3)

Drizzle schema for projects, defects, push_subscriptions (C8); generated
migration; a defects repository (createDefect / listRecentDefects); a
programmatic migrator; and a db:verify script. section_id is a plain string
referencing in-code board ids, no FK (ADR 0001). Verified against real
Postgres: migration applies, a defect round-trips, /api/health reports db up.

server/db/migrations/meta/_journal.json

@@ -0,0 +1,13 @@
+{
+  "version": "7",
+  "dialect": "postgresql",
+  "entries": [
+    {
+      "idx": 0,
+      "version": "7",
+      "when": 1779913917235,
+      "tag": "0000_loving_black_bird",
+      "breakpoints": true
+    }
+  ]
+}