extract speech-to-text into its own plugin

Moves platform STT out into a plugin that owns the whole whisper.cpp contract: sidecar,
config (a JSON file under DATA_PATH/transcribe/, validated against the server before
storing), a thin proxy router, a skill so an agent knows the contract without being told,
and a script-mode file-browser task (not agentic — no model turn per audio file).

sidecar/transcribe.ts and its test moved unchanged from src/servers/api/stt/ — every
constant in it has a reason attached and none of it was touched.

The platform-side removal (routes, dead useAudioRecording path, Settings screen, locale
keys) lands in a separate, uncommitted change in the platform repo for review.

Not yet reachable from the file browser: the platform does not load tasks from a plugin's
directory yet (skills/affordances/notifications do). Ships anyway per instructions.

Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

PLUGIN.md

@@ -0,0 +1,77 @@
+# Transcribe — the extraction record
+
+Extracted from the platform on **2026-08-24**. `plugins/EXTRACTING-A-PLUGIN.md` is the runbook; this
+file is what it cost.
+
+## What moved
+
+| Was                                          | Is now                                  |
+| --------------------------------------------- | ---------------------------------------- |
+| `src/servers/api/stt/transcribe.ts`           | `sidecar/transcribe.ts` — unchanged      |
+| `src/servers/api/stt/transcribe.test.ts`      | `sidecar/transcribe.test.ts` — unchanged |
+| `src/servers/api/server-settings/stt.ts`      | `sidecar/config.ts` — rewritten          |
+
+`sidecar/transcribe.ts` is the reason this extraction exists at all: 416 lines of tuning — the two-pass
+detect-then-transcribe, 25 language priming prompts, the VAD widening, the paragraphing — each with a
+reason in its own comment, and none of it touched. Moving it, not rewriting it, was the instruction and
+the only defensible one: every constant in that file was chosen against a real recording at some point,
+and there is no way to re-derive that from reading the code cold.
+
+## What did not move unchanged: config
+
+The platform kept a single admin-only setting, `server-settings/stt` — one row in a JSON blob
+(`readServerSettings`/`writeServerSettings`), gated by the `server-admin` permission and reachable only
+by the owner. That shape does not exist here to move into: a plugin's config is its own file, not a slot
+in the platform's settings blob, and this plugin's own permission (`transcribe`) is grantable to anyone,
+not owner-only.
+
+So `sidecar/config.ts` is new, not moved: a JSON file under `DATA_PATH/transcribe/`, following the
+`DATA_PATH/<plugin>/` convention `plugins/music/sidecar/indexer.ts` established, with the same
+validate-before-store behaviour the old `/server-settings/stt/test` route had (an empty multipart POST to
+`/inference` — Whisper always rejects it, but any response at all means the server exists).
+
+**Deliberately not owner-only.** Photos' `/_config` holds a real credential (an Immich API key) and is
+still reachable by any account holding the permission at write; jellyfin's manifest, despite the
+`ownerOnly` field existing for exactly this shape, does not set it either. A Whisper URL is not a
+credential — there is nothing to steal by reading it, and nothing more dangerous than "the transcriptions
+go to a different server" by changing it — so this follows the same precedent rather than inventing a
+narrower one.
+
+## What the platform lost
+
+Deleted, not commented — see the platform-side diff for the full list: `src/servers/api/stt/`, the
+`server-settings/stt` router and its mount, `POST /chat/stt`, the dead `useAudioRecording` STT path
+(`blobToWav` stays; `DictateDialog.tsx` still needs it for something that was never STT — see below),
+`POST /file-browser/transcribe` and the FileViewer handler behind the button that was already hidden, the
+Settings → Speech to Text screen, and the orphaned locale keys across all six `officer-web` locales.
+
+**One thing found and left alone.** `DictateDialog.tsx` in the file browser imports `blobToWav` from the
+same file `useAudioRecording`'s dead STT path lived in. It records audio and uploads the raw `.wav` — it
+never called Whisper, was never part of this feature, and stays in the platform exactly as it is. Deleting
+the whole file would have taken it down as collateral.
+
+## The task: script, not agentic
+
+The worked reference this shipped against (`~/dockers/officer.dev/seed-archive/tasks/transcribe-audio-file/`
+on alpha) is agentic: it runs its own detect-language pass before transcribing, and generates an
+archive-folder title from the transcription's contents. Both are wrong for a script task and were dropped
+on purpose rather than carried over — the detect step duplicates what the plugin's route already does
+server-side, and a generated title needs a model turn, which is the entire thing "script, not agentic" was
+asked for to avoid spending per file. The filing behaviour (a dated, slugged sibling directory, original
+moved in, transcript saved beside it) is the part worth keeping, so it survived; the slug now comes from
+the original filename instead of a generated title.
+
+## What is NOT wired up yet
+
+**The platform does not load tasks from a plugin's directory.** Skills, affordances and notifications are
+read from `plugins/<name>/` at runtime (`docs/plugin-capabilities.md`); tasks are not — `task-files.ts`
+only reads `$OFFICER_ITEMS_DIR/tasks/`. So `tasks/transcribe-audio-file/` ships here, is correct, and will
+not appear in the file browser's right-click menu until that loader lands. Not a defect in this plugin;
+recorded so nobody spends an evening looking for why it is missing.
+
+## Still open
+
+- **No `assets/icon.png`.** Falls back to the `AudioLines` lucide glyph.
+- **Single Whisper server, not a registry.** Unlike `photos_config` or `jellyfin_servers`, there is
+  exactly one URL and no way to keep a second on hand. Revisit if that ever turns out to be wanted —
+  nothing here forecloses it, but nothing asked for it either.