Standalone Shonar Desktop: vendor portable sources + local engine; decouple from ~/Projects/Shonar

- shared/ = portable Android-origin sources vendored from deferred/desktop-server
  (app/build.gradle.kts srcDir repointed; PlaybackController.kt excluded as Android-only)
- backend/ = bundled-lite engine (SQLite + inline queue); .venv symlinked from the
  old checkout, PYTHONPATH pins THIS backend's code over any editable install
- repoRoot() resolves this project dir (env SHONAR_REPO still wins); desktop-dev.sh
  watches shared/ + backend/
- Verified: :app:compileKotlin + :app:test green (23 tests); engine boots on :8010,
  self-migrates, /healthz ok

backend/shonar/api/v1/models.py

@@ -0,0 +1,132 @@
+"""Transcription model registry + global default (Stage 1).
+
+- GET /models — supported models with display metadata, download and
+  availability status, and which is the default.
+- GET /models/default — the current global default model name.
+- PUT /models/default — change the global default (affects future
+  recordings only; saved per-recording models are never rewritten).
+- POST /models/{name}/download — fetch a model into the local cache
+  (needs internet once; runs synchronously and may take minutes for
+  large models).
+"""
+
+from __future__ import annotations
+
+import asyncio
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel, Field
+
+from shonar.api.deps import CurrentUser, SessionDep
+from shonar.services.ai import ProviderConfigError
+from shonar.services.ai.model_registry import (
+    SUPPORTED_TRANSCRIPTION_MODELS,
+    get_global_default_model,
+    is_faster_whisper_installed,
+    is_model_downloaded,
+    set_global_default_model,
+    validate_model_name,
+)
+
+router = APIRouter(tags=["models"])
+
+
+class TranscriptionModelOut(BaseModel):
+    name: str
+    display_name: str
+    description: str
+    params: str
+    approx_memory: str
+    relative_speed: str
+    is_default: bool
+    downloaded: bool
+    available: bool
+
+
+class ModelsOut(BaseModel):
+    default_model: str
+    faster_whisper_installed: bool
+    models: list[TranscriptionModelOut]
+
+
+class DefaultModelUpdate(BaseModel):
+    model: str = Field(min_length=1, max_length=32)
+
+
+class DefaultModelOut(BaseModel):
+    default_model: str
+
+
+async def _models_out(session: SessionDep) -> ModelsOut:
+    default = await get_global_default_model(session)
+    installed = is_faster_whisper_installed()
+    return ModelsOut(
+        default_model=default,
+        faster_whisper_installed=installed,
+        models=[
+            TranscriptionModelOut(
+                name=info.name,
+                display_name=info.display_name,
+                description=info.description,
+                params=info.params,
+                approx_memory=info.approx_memory,
+                relative_speed=info.relative_speed,
+                is_default=info.name == default,
+                downloaded=is_model_downloaded(info.name),
+                available=installed and is_model_downloaded(info.name),
+            )
+            for info in SUPPORTED_TRANSCRIPTION_MODELS.values()
+        ],
+    )
+
+
+@router.get("/models", response_model=ModelsOut)
+async def list_models(user: CurrentUser, session: SessionDep):
+    return await _models_out(session)
+
+
+@router.get("/models/default", response_model=DefaultModelOut)
+async def get_default_model(user: CurrentUser, session: SessionDep):
+    return DefaultModelOut(default_model=await get_global_default_model(session))
+
+
+@router.put("/models/default", response_model=DefaultModelOut)
+async def put_default_model(body: DefaultModelUpdate, user: CurrentUser, session: SessionDep):
+    try:
+        name = await set_global_default_model(session, body.model)
+    except ProviderConfigError as e:
+        raise HTTPException(422, str(e)) from None
+    return DefaultModelOut(default_model=name)
+
+
+@router.post("/models/{name}/download", response_model=TranscriptionModelOut)
+async def download_model(name: str, user: CurrentUser, session: SessionDep):
+    try:
+        clean = validate_model_name(name)
+    except ProviderConfigError as e:
+        raise HTTPException(422, str(e)) from None
+    if not is_faster_whisper_installed():
+        raise HTTPException(
+            501,
+            "faster-whisper is not installed on this server "
+            "(pip install shonar-backend[faster-whisper]).",
+        )
+    from shonar.services.ai.faster_whisper import _load_model
+
+    try:
+        await asyncio.to_thread(_load_model, clean)
+    except Exception as e:  # noqa: BLE001 — surface download failures plainly
+        raise HTTPException(500, f"Model download failed: {e}") from None
+    default = await get_global_default_model(session)
+    info = SUPPORTED_TRANSCRIPTION_MODELS[clean]
+    return TranscriptionModelOut(
+        name=info.name,
+        display_name=info.display_name,
+        description=info.description,
+        params=info.params,
+        approx_memory=info.approx_memory,
+        relative_speed=info.relative_speed,
+        is_default=info.name == default,
+        downloaded=is_model_downloaded(clean),
+        available=is_model_downloaded(clean),
+    )