fix: major bug audit + fixes — honest PLAN.md

Critical bugs fixed:
- SELECT now returns actual row data (was returning empty arrays)
- WHERE filter evaluation now works (was pass-through stub)
- ORDER BY sorting now works (was no-op)
- UPDATE execution implemented (was no-op stub)
- DELETE uses WHERE filter (was key-match only)
- B-Tree point reads return actual row data (was returning count only)
- EXPLAIN returns plan string (was computed then discarded)
- UNIQUE constraint uses B-Tree index (was memtable scan only)
- DEFAULT values work for int/bool/float (was string-only)
- HTTP /query returns real JSON rows with columns
- Docker healthcheck uses wget (Alpine has no curl)

Updated PLAN.md with honest status:
- Marked what's truly done vs stub vs not implemented
- Honest score: 8/10 (not 9.5/10)
- Clear list of what actually works in production

All 216 tests pass

docker-compose.yml

@@ -14,7 +14,7 @@ services:
       - BARADB_HTTP_PORT=8080
       - BARADB_WS_PORT=8081
     healthcheck:
-      test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
+      test: ["CMD", "wget", "-q", "--spider", "http://localhost:8080/health"]
       interval: 10s
       timeout: 5s
       retries: 3