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/main.py

@@ -0,0 +1,79 @@
+"""S.H.O.N.A.R. FastAPI application entrypoint.
+
+Run (dev):  uvicorn shonar.main:app --reload --port 8000
+"""
+
+from __future__ import annotations
+
+import logging
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
+from slowapi import _rate_limit_exceeded_handler
+from slowapi.errors import RateLimitExceeded
+
+from shonar import __version__
+from shonar.api.v1 import api_router
+from shonar.core.config import get_settings
+from shonar.core.ratelimit import limiter
+from shonar.db.session import dispose_engine, get_engine
+
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger("shonar")
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    settings = get_settings()
+    get_engine()  # validate URL parses; connections are lazy
+    for warning in settings.validate_production():
+        logger.warning("CONFIG: %s", warning)
+    if settings.auto_migrate:
+        from shonar.db.migrate import upgrade_head
+
+        await upgrade_head(settings.database_url)
+    inline = settings.queue_backend.strip().lower() == "inline"
+    if inline:
+        from shonar.services import inline_queue
+
+        await inline_queue.start()
+    yield
+    if inline:
+        from shonar.services import inline_queue
+
+        await inline_queue.stop()
+    await dispose_engine()
+
+
+app = FastAPI(
+    title="SHONAR API",
+    description=(
+        "SHONAR — Self-hosted Oral Notes and Audio Recorder. REST API. "
+        "All data stays on your server."
+    ),
+    version=__version__,
+    lifespan=lifespan,
+    # Interactive docs at the conventional paths.
+    docs_url="/docs",
+    redoc_url="/redoc",
+    openapi_url="/openapi.json",
+)
+
+app.state.limiter = limiter
+app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler)
+
+
+@app.exception_handler(Exception)
+async def unhandled_exception_handler(request: Request, exc: Exception):
+    """Safe error surface: log details server-side, never leak internals."""
+    logger.exception("Unhandled error on %s %s", request.method, request.url.path)
+    return JSONResponse(status_code=500, content={"detail": "Internal server error"})
+
+
+app.include_router(api_router)
+
+
+@app.get("/")
+async def root():
+    return {"app": "SHONAR", "docs": "/docs", "health": "/api/v1/healthz"}