feat(search): recherche semantique - embeddings vectoriels + hybride RRF (#70)

README.md

@@ -54,7 +54,7 @@
 - **🗺️ Interactive Graph View** — Canvas force-directed with Barnes-Hut O(n log n), filters (tag, type), depth, focus mode, navigation history ←→↑, export PNG, preview on hover (Ctrl+click)
 - **🗂️ Multi-vault** : View multiple Obsidian vaults simultaneously
 - **🌳 Tree Navigation** : Browse your folders and files in the sidebar
-- **🔍 Advanced Search** : TF-IDF search engine with French stemming, accent normalization, highlighted snippets, facets, pagination, and sorting
+- **🔍 Advanced Search** : TF-IDF search engine with French stemming, accent normalization, highlighted snippets, facets, pagination, and sorting — plus an optional **semantic search** (embeddings via `all-MiniLM-L6-v2`, hybrid TF-IDF + RRF fusion) toggled with `~` ([details](docs/features/semantic-search.md))
 - **💡 Smart Autocomplete** : Suggestions for files, tags, and history with keyboard navigation
 - **🧩 Query Syntax** : Operators `tag:`, `#`, `vault:`, `title:`, `path:`, `ext:` with visual chips
 - **📜 Search History** : Persisted in localStorage (max 50 entries, LIFO, deduplicated)
@@ -708,7 +708,7 @@ ObsiGate exposes a complete REST API :
 | `/api/file/{vault}/download?path=` | Download a file | GET | Yes |
 | `/api/file/{vault}/save?path=` | Save a file | PUT | Yes |
 | `/api/file/{vault}?path=` | Delete a file | DELETE | Yes |
-| `/api/search/advanced` | Advanced TF-IDF search | GET | Yes |
+| `/api/search/advanced` | Advanced TF-IDF search (+ `semantic=true` for hybrid) | GET | Yes |
 | `/api/suggest` / `/api/tags/suggest` | Autocomplete | GET | Yes |
 | `/api/tags?vault=` | Unique tags with counters | GET | Yes |
 | `/api/index/reload` | Force a rescan of vaults | GET | Admin |
@@ -802,6 +802,10 @@ Operators are combinable: `tag:linux vault:IT ext:md server web` searches for "s
 - **Sorting** : By relevance (TF-IDF) or modification date
 - **Visual chips** : Active filters are shown as removable colored chips
 - **History** : Last 50 searches are stored in localStorage
+- **Semantic search** (optional) : Toggle `~` (or `Alt+S`) fuses the TF-IDF ranking with an
+  embedding-based ranking (RRF). Works out of the box with a dependency-free hashing embedder;
+  install `backend/requirements-semantic.txt` and/or set `OBSIGATE_EMBEDDING_*` for real
+  `all-MiniLM-L6-v2` embeddings. See [docs/features/semantic-search.md](docs/features/semantic-search.md).
 
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