feat(defects): read API — feed, per-section counts and history (T6)

GET /api/defects returns a newest-first feed joined to the project name,
bounded by limit; ?section=ID narrows to one section's history. GET
/api/defects/counts returns { sectionId: n } for the weak-point map. Adds a
(section_id, created_at) index and a db:seed script; ~2k rows query in ~20ms.

server/api/defects/counts.get.ts

@@ -0,0 +1,7 @@
+import { getDb } from '../../db/client'
+import { countDefectsBySection } from '../../db/repositories/defects'
+
+// Per-section defect counts `{ sectionId: n }` for the weak-point map (F4/F6).
+export default defineEventHandler(async () => {
+  return countDefectsBySection(getDb())
+})