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/index.json

@@ -36,7 +36,7 @@
       "project": null,
       "subdir": null,
       "video": "",
-      "tldr": "Google a lansat **Open Knowledge Format (OKF)** — un standard pentru organizarea knowledge base-urilor astfel încât agenții AI să navigheze mai eficient. Se bazează pe pattern-ul LLM Wiki al lui Andre..."
+      "tldr": "Un video prezintă **Open Knowledge Format (OKF)** — un format *propus* pentru organizarea knowledge base-urilor astfel încât agenții AI să navigheze mai eficient. (Vezi Status: nu e confirmat ca relea..."
     },
     {
       "file": "notes-data/youtube/2026-06-25_google-agentic-engineering-masterclass.md",
@@ -9577,8 +9577,8 @@
       "title": "Proiect: Vending Master - Integrare Website → ROA",
       "date": "2026-01-30",
       "tags": [
-        "integrare",
-        "vending-master"
+        "vending-master",
+        "integrare"
       ],
       "domains": [
         "work"