feat: garde-fous d'écriture des classeurs Excel #153 (P0)

L'édition d'un .xlsx pouvait détruire une partie du classeur, le
concurrencer en silence, ou diffuser une injection de formule.

- BUG-085 : inspect_workbook() détecte ce qu'un round-trip openpyxl perd
  (valeurs calculées en cache, slicers, contrôles, connexions, custom
  XML, signature, commentaires enrichis, macros) → xlsx_lossy_features
  exposé en lecture, bandeau FR/EN, et 409 xlsx_lossy_content sans
  `force` (confirmation explicite puis reprise). Périmètre réel
  revalidé : graphiques, images et TCD survivent au round-trip.
- BUG-086 : écriture atomique (fichier .tmp + os.replace) : un plantage
  ne peut plus tronquer le classeur, le backup reste intact.
- BUG-087 : verrou par fichier autour du read-modify-write (timeout 15 s,
  409 conflict) ; endpoint xlsx/save devenu synchrone pour que
  l'attente s'exécute dans le threadpool.
- BUG-088 : une saisie en '=' ou '@' est stockée en texte, sauf opt-in
  `allow_formula` ou le bouton f(x) de la visionneuse. Le handler
  ServiceError expose désormais code + details, que api() propage.
- BUG-084 : la suppression d'une vault purge enfin l'index inversé
  (documents fantômes qui continuaient de matcher) et is_stale() devient
  is_ready(), le nom étant trompeur (la staleness n'existe plus).

Tests : 1390 pytest, 10 JSDOM (xlsx-viewer.test.mjs, branché au CI),
3 E2E Playwright, suite E2E complète verte, ruff/mypy 0.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <[email protected]>

README.md

@@ -2,7 +2,7 @@
 
 **Ultra-light web gateway for your Obsidian vaults** — Access, browse, and search all your Obsidian notes from any device via a modern, responsive web interface.
 
-[![Version](https://img.shields.io/badge/Version-2.28.16-blue.svg)]()
+[![Version](https://img.shields.io/badge/Version-2.29.0-blue.svg)]()
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 [![Docker](https://img.shields.io/badge/Docker-Ready-blue.svg)](https://www.docker.com/)
 [![Python](https://img.shields.io/badge/Python-3.11+-green.svg)](https://www.python.org/)
@@ -21,7 +21,7 @@ Step-by-step **user guides** live in [`docs/GUIDES/`](docs/GUIDES/):
 | Guide | What it covers |
 |---|---|
 | 🚀 [Getting Started](docs/GUIDES/PRISE_EN_MAIN.md) | First run, interface, navigation, vaults, shortcuts |
-| 🔍 [Search, PDF & Excalidraw](docs/GUIDES/RECHERCHE_PDF_EXCALIDRAW.md) | Query syntax, semantic search, PDF viewer, diagrams |
+| 🔍 [Search, PDF, Excel & Excalidraw](docs/GUIDES/RECHERCHE_PDF_EXCALIDRAW.md) | Query syntax, semantic search, PDF/Excel viewers, diagrams |
 | 🤖 [AI Assistant & Forge](docs/GUIDES/ASSISTANT_IA_FORGE.md) | Providers, AI editor, BooksLM, Forge, `@` / `/` commands |
 | 📝 [Editing & Collaboration](docs/GUIDES/COLLABORATION.md) | Simultaneous editing, remote cursors, persistence |
 | 📱 [PWA & Offline](docs/GUIDES/PWA_HORS_LIGNE.md) | Install as an app, offline cache, sync queue, push |
@@ -84,7 +84,7 @@ Step-by-step **user guides** live in [`docs/GUIDES/`](docs/GUIDES/):
 - **🖼️ Obsidian Images** : Full support for all Obsidian image syntaxes with intelligent resolution
 - **🎬 Audio & video** : Built-in HTML5 players (`.mp3 .wav .flac .mp4 .webm`…) with HTTP Range streaming (play, seek, fullscreen) and **persistent playback** (floating mini-player / mini video window, return to media or stop anytime, lock-screen controls via Media Session), falling back to download when the format is not playable in the browser
 - **🎨 Excalidraw Diagrams** : Native viewer/editor for `.excalidraw` and `.excalidraw.md` files (sandboxed iframe, autosave, dark/light theme, diagram text indexed for search)
-- **📊 Excel Spreadsheets** : `.xlsx` files open in a dedicated viewer — one table per sheet with tabs, A1 headers and inline cell editing (`PUT /api/file/{vault}/xlsx/save`, automatic backup), plus download of the original file
+- **📊 Excel Spreadsheets** : `.xlsx` files open in a dedicated viewer — one table per sheet with tabs, A1 headers and inline cell editing (`PUT /api/file/{vault}/xlsx/save`, automatic backup, atomic write), plus download of the original file. Workbooks holding elements ObsiGate cannot preserve (cached values, slicers, form controls, signature…) show a **warning** and ask for confirmation before saving; a value starting with `=` or `@` is stored as text unless the `f(x)` toggle is enabled
 - **🎨 Syntax Highlight** : Syntax highlighting for code blocks
 - **🌓 Light/Dark Theme** : Toggle persisted in localStorage
 - **📡 Real-time Sync** : Automatic file monitoring via watchdog with incremental index updates
@@ -804,7 +804,7 @@ curl "http://localhost:2020/api/file/Recipes?path=pizza.md"
 
 ## 🔍 Advanced Search
 
-> 📖 Full guide: [Search, PDF & Excalidraw](docs/GUIDES/RECHERCHE_PDF_EXCALIDRAW.md)
+> 📖 Full guide: [Search, PDF, Excel & Excalidraw](docs/GUIDES/RECHERCHE_PDF_EXCALIDRAW.md)
 
 ### Query Syntax
 
@@ -1151,8 +1151,8 @@ This project is licensed under the **MIT License** - see the [LICENSE](LICENSE)
 
 ## 📝 Changelog
 
-See [CHANGELOG.md](./CHANGELOG.md) for the complete version history (v1.0.0 → v2.28.16).
+See [CHANGELOG.md](./CHANGELOG.md) for the complete version history (v1.0.0 → v2.29.0).
 
 ---
 
-*Project: ObsiGate | Version: 2.28.16 | Last updated: September 2026*
+*Project: ObsiGate | Version: 2.29.0 | Last updated: September 2026*