stt leaves the platform for the transcribe plugin

Speech-to-text is now plugins/transcribe — sidecar, its own config, its own
skill and a task for the file browser's context menu. The transcription logic
moved BYTE FOR BYTE: 416 lines whose every decision has a reason attached, from
the two-pass detect-then-transcribe to the 25 language priming prompts to
timeout:false. Verified identical rather than assumed.

Removed here: api/stt/, server-settings/stt.ts and its mount, POST /chat/stt,
POST /file-browser/transcribe, the FileViewer handler behind the button hidden
last release, the Settings screen, the dead useAudioRecording hook and the
orphaned locale keys across all six locales.

blobToWav stayed. It lived in the same file as the dead hook and is still used
by DictateDialog — unrelated to STT, and deleting by file rather than by use is
how that would have gone.

No permission entry to remove: STT never had one, living under server-admin,
chat and files. The registry count is unchanged and docs:check is green.

The plugin ships a task that will not appear in the menu yet — the platform
loads a plugin's skills, affordances and notifications from its own directory
but not its tasks. That loader is the remaining piece of docs/plugin-capabilities.md
and is deliberately not built here.

1426 pass, tsgo clean, 18 plugins discovered with none broken.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

src/apps/officer-web/locales/fr-FR.json

@@ -145,10 +145,6 @@
         "label": "Synthèse vocale",
         "description": "Fournisseur et voix pour la synthèse vocale"
       },
-      "stt": {
-        "label": "Reconnaissance vocale",
-        "description": "URL du serveur Whisper"
-      },
       "ocr": {
         "label": "OCR",
         "description": "Modèle de vision pour l'extraction de texte"
@@ -234,12 +230,6 @@
         "saveFailed": "Échec de l'enregistrement des paramètres OCR",
         "reachable": "Le serveur du modèle de vision est accessible"
       },
-      "stt": {
-        "serverUrl": "URL du serveur Whisper",
-        "saved": "Paramètres de reconnaissance vocale enregistrés",
-        "saveFailed": "Échec de l'enregistrement des paramètres de reconnaissance vocale",
-        "reachable": "Le serveur Whisper est accessible"
-      },
       "tts": {
         "openaiCompatible": "Compatible OpenAI (Kokoro, OpenAI, etc.)",
         "elevenLabs": "ElevenLabs",