feat(memory): hybrid retrieval — navigation index.md + RAG hardening

Expose a navigation layer to the agent and harden RAG, after analyzing the
OKF note and testing on the real KB.

- memory_search.search(): dedupe best-chunk-per-file (a relevant note can no
  longer be buried by another file's chunks) + keyword fallback tagged
  degraded:True when Ollama is unreachable (no more hard crash).
- update_notes_index.py: emit per-folder index.md + root router; prune empty
  folders; fix latent subcategory->project bug.
- Exclude generated index.md from RAG rglob (reindex/incremental) + indexer
  scans + heartbeat freshness check (prevents self-pollution / reindex thrash).
- CLAUDE.md: reframe memory as hybrid (navigation first, RAG for fuzzy recall).
- Delete stale orphan kb/youtube/index.json; correct the OKF source note.
- Tests: dedup, keyword fallback, index.md exclusion. Plan + review in docs/.

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

memory/kb/health/index.md

@@ -0,0 +1,16 @@
+# Index — health/
+
+> 6 note. Citește acest index întâi; deschide doar fișierele relevante.
+
+- **[Checklist Post cu Apă](checklist-post-apa.md)**  `@health #post #water-fasting #detox`
+  *Notă: Acest checklist e pentru referință. Consultă un specialist înainte de posturi lungi.*
+- **[Exercise Snacks Protocol - Marius](exercise-snacks-protocol.md)**
+  - <https://health.clevelandclinic.org/exercise-snacks>
+- **[Protocol Post 3 Zile - Versiune Veggie (România)](protocol-post-3-zile-veggie.md)**  `@health`
+  - **Next review:** După primul fast completat
+- **[Protocol Post 3 Zile - Implementare Practică](protocol-post-3-zile.md)**  `@health`
+  - **Next review:** După primul fast completat
+- **[Protocol Post 7 Zile - Versiune Veggie (România)](protocol-post-7-zile-veggie.md)**  `@health`
+  - **Next review:** După primul fast completat
+- **[Protocol Post 7 Zile - Implementare Practică (Acasă)](protocol-post-7-zile.md)**  `@health`
+  - **Next review:** După primul fast completat