v1.5.0: entry-dedup in één query + conditional get (ETag/Last-Modified)

- filter_entries: één SELECT per feed i.p.v. per-entry EXISTS (1082 queries → 20)
- feed.etag/last_modified (migratie v9); parse_feed stuurt If-None-Match/If-Modified-Since, 304 → None
- _poll_once telt unchanged (304-feeds); summary-regel uitgebreid met unchanged
- _poll_feeds re-raised CancelledError (reload-stapeling duplicaten) + handler-cleanup

buzzrss/migrations.py

@@ -99,3 +99,9 @@ async def upgrade_v7(conn: Connection) -> None:
 @upgrade_table.register(description="Add paywalled flag to entries")
 async def upgrade_v8(conn: Connection) -> None:
     await conn.execute("ALTER TABLE entry ADD COLUMN paywalled BOOLEAN NOT NULL DEFAULT false")
+
+
+@upgrade_table.register(description="Add conditional-fetch headers to feeds")
+async def upgrade_v9(conn: Connection) -> None:
+    await conn.execute("ALTER TABLE feed ADD COLUMN etag TEXT DEFAULT ''")
+    await conn.execute("ALTER TABLE feed ADD COLUMN last_modified TEXT DEFAULT ''")