Engine venv is now local to this repo (uv venv + editable install of this backend)

- backend/.venv was a symlink into ~/Projects/Shonar; replaced with a real
  local venv built fully offline from the uv cache (deps pinned to the
  versions the app was tested with: fastapi, uvicorn, sqlalchemy,
  aiosqlite, alembic, faster-whisper 1.2.1, dev extras)
- editable install resolves 'shonar' to THIS backend/ (verified via
  shonar.__file__); PYTHONPATH pin kept as a belt
- verified standalone: with ~/Projects/Shonar renamed away, engine boots,
  self-migrates (alembic head m8models000001), /healthz + /readyz ok, and
  full register -> upload -> finalize -> list -> audio-download roundtrip
  passes (sha256 match)

app/src/main/kotlin/com/shonar/desktop/DesktopState.kt

@@ -297,8 +297,9 @@ class DesktopState(private val appDir: File = defaultAppDir()) {
                     fresh
                 }
                 val env = mutableMapOf(
-                    // The .venv may be shared (symlink) whose editable install
-                    // points elsewhere — PYTHONPATH makes THIS backend win.
+                    // backend/.venv is local to this project (uv venv, editable
+                    // install of THIS backend). PYTHONPATH kept as a belt: it
+                    // pins this code over any other shonar on the interpreter.
                     "PYTHONPATH" to backend.absolutePath,
                     "SHONAR_SECRET_KEY" to secret,
                     // Bundled-lite: one process, SQLite, in-process queue,