feat(5.18): VERIFY+CLOSE — US-007 badge sursa + fix findings code-review

VERIFY PASS pe corpus k-NN exemple etichetate (seed real 17181 Haiku, comis
in 756f777): suita 1392 passed, 1 deselected (live); smoke init_db seeder
(17181/NUL=2200/idempotent); toate codurile in nomenclator.

US-007 (cerere user la CLOSE) — badge sursa pe sugestia fuzzy din editor:
- _mapari.html: chip confirmat (GOLD) / similar (SILVER+k-NN) / non-operatie (NUL)
- base.html: .sugg-sursa--{confirmat,similar,nul} pe tokeni de tema (color-mix)
- routes.py: cheia `nul` adaugata in surse_sugestie default (finding cross-file)
- tests/test_web_badge_sursa.py: gold/silver/nul/fara-sursa (4 teste)
- E2E render live verificat in serverul real (/_fragments/mapari)

CLOSE /code-review high (main..HEAD, 3 finder x 8 unghiuri) — runtime curat,
invariant #13 intact; 3 findings low/cosmetic REPARATE + lock-uite:
- shared_store.seed_suggestions: cod whitespace -> NULL (era ''), + test lock
- genereaza_seed.py: with open(...) in loc de open().read() (FD leak tool offline)
- embeddings.py: docstring-uri aliniate la [{cod, is_nul, similaritate}]

ROADMAP: 5.18 LIVRAT. PRD: raport VERIFY/CLOSE scris.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/web/routes.py

@@ -1247,7 +1247,7 @@ def _nemapate_pentru_submission(row, nomenclator: list[dict], conn=None) -> list
             "denumire": item.get("denumire"),
             "suggestions": suggest_codes(item.get("denumire"), nomenclator, limit=5),
             "sugestie_principala": None,
-            "surse_sugestie": {"gold_partajat": None, "silver": None, "embedding": None},
+            "surse_sugestie": {"gold_partajat": None, "silver": None, "embedding": None, "nul": False},
         }
         # L14-S6: imbogatire cu GOLD partajat > SILVER > embeddings (SUGGESTION-ONLY, #13)
         if conn is not None: