radio: add /api/db.sqlite for offline laptop sync

Streams the read-only archive.db over the same Tailscale-routed port
as the search service. Companion to azcomputerguru/radio-archive-portable
which curl-fetches from this endpoint and runs locally on the laptop.

Disclosure equivalent to /api/search (which already exposes every
transcript), so no auth added. Deployed to Jupiter; verified GET
returns 60 MB SQLite blob with all 1,405 classifier rows intact.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

projects/radio-show/audio-processor/server/main.py

@@ -20,7 +20,7 @@ from contextlib import asynccontextmanager
 from pathlib import Path
 
 from fastapi import FastAPI, HTTPException, Query
-from fastapi.responses import HTMLResponse
+from fastapi.responses import FileResponse, HTMLResponse
 
 DB_PATH = os.environ.get("ARCHIVE_DB", "/data/archive.db")
 PORT = int(os.environ.get("PORT", "8765"))
@@ -218,6 +218,23 @@ def stats():
     return {"counts": counts, "by_year": by_year}
 
 
+@app.get("/api/db.sqlite")
+def download_db():
+    """Stream the read-only archive.db for offline laptop sync.
+
+    Anyone who can reach /api/search can already read every transcript,
+    so exposing the underlying SQLite file adds no meaningful disclosure.
+    Sync side: curl -o archive.db <host>:<port>/api/db.sqlite
+    """
+    if not Path(DB_PATH).exists():
+        raise HTTPException(404, "archive db not present")
+    return FileResponse(
+        DB_PATH,
+        media_type="application/vnd.sqlite3",
+        filename="archive.db",
+    )
+
+
 @app.get("/", response_class=HTMLResponse)
 def index():
     return INDEX_HTML