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/migrations/versions/m8models000001_model_support.py

@@ -0,0 +1,69 @@
+"""per-recording transcription model + job progress + app settings
+
+Revision ID: m8models000001
+Revises: fts0000000001
+
+- recordings.transcription_model (nullable; NULL = server default)
+- processing_jobs.stage / processing_jobs.progress (display-only)
+- app_settings table (global default model, …)
+"""
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+revision: str = 'm8models000001'
+down_revision: str | None = 'fts0000000001'
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def _json_type() -> sa.types.TypeEngine:
+    """JSONB on PostgreSQL, plain JSON on SQLite (desktop bundled engine)."""
+    if op.get_context().dialect.name == "postgresql":
+        return postgresql.JSONB(astext_type=sa.Text())
+    return sa.JSON()
+
+
+def upgrade() -> None:
+    op.add_column(
+        "recordings",
+        sa.Column("transcription_model", sa.String(length=32), nullable=True),
+    )
+    op.add_column(
+        "upload_sessions",
+        sa.Column("transcription_model", sa.String(length=32), nullable=True),
+    )
+    op.add_column(
+        "processing_jobs",
+        sa.Column("stage", sa.String(length=32), nullable=True),
+    )
+    op.add_column(
+        "processing_jobs",
+        sa.Column("progress", sa.Integer(), nullable=True),
+    )
+    op.create_table(
+        "app_settings",
+        sa.Column("key", sa.String(length=120), nullable=False),
+        sa.Column(
+            "value",
+            _json_type(),
+            nullable=False,
+        ),
+        sa.Column("id", sa.Uuid(), nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("key"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("app_settings")
+    op.drop_column("processing_jobs", "progress")
+    op.drop_column("processing_jobs", "stage")
+    op.drop_column("upload_sessions", "transcription_model")
+    op.drop_column("recordings", "transcription_model")