fix(vwb): noms workflows lisibles + bibliothèque captures persistante

CSS : le dropdown héritait color:white du header → forcé #212121
sur .workflow-dropdown et .dropdown-item .item-name

Bibliothèque : migration localStorage → backend (capture_library.json)
- GET/POST /api/v3/capture/library (max 50 captures)
- loadLibraryAsync() charge depuis backend, fallback localStorage
- saveLibrary() écrit dans les deux (localStorage + backend)
- capture_library.json gitignored

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -95,6 +95,7 @@ archives/
 
 # === Données runtime (sessions, learning, buffer, config local) ===
 data/
+**/capture_library.json
 .hypothesis/
 .deps_installed
 # Buffers SQLite locaux (streamer, cache)