Fail GitHub scans on asset errors and drop sync state with its remote

- fail the scan when a release asset fails to derive or insert, so the ETag is kept and the retry re-derives it
- cascade sync-state rows on remote delete (migration 0003)

migrations/0003_github_sync_state_cascade.sql

@@ -0,0 +1,12 @@
+-- Sync state is dropped with its remote, so a recreated remote of the same name
+-- starts with no inherited ETag or timing. NOT VALID skips checking rows left by
+-- remotes deleted before this migration, which would otherwise fail it.
+ALTER TABLE github_rpm_sync_state    DROP CONSTRAINT IF EXISTS github_rpm_sync_state_remote_fk;
+ALTER TABLE github_rpm_sync_state    ADD CONSTRAINT github_rpm_sync_state_remote_fk
+	FOREIGN KEY (remote_name) REFERENCES remotes(name) ON DELETE CASCADE NOT VALID;
+ALTER TABLE github_deb_sync_state    DROP CONSTRAINT IF EXISTS github_deb_sync_state_remote_fk;
+ALTER TABLE github_deb_sync_state    ADD CONSTRAINT github_deb_sync_state_remote_fk
+	FOREIGN KEY (remote_name) REFERENCES remotes(name) ON DELETE CASCADE NOT VALID;
+ALTER TABLE github_alpine_sync_state DROP CONSTRAINT IF EXISTS github_alpine_sync_state_remote_fk;
+ALTER TABLE github_alpine_sync_state ADD CONSTRAINT github_alpine_sync_state_remote_fk
+	FOREIGN KEY (remote_name) REFERENCES remotes(name) ON DELETE CASCADE NOT VALID;