fix: add ON DELETE CASCADE to uploads FK on snapshot_id (#44)

The `uploads` table's foreign key on `snapshot_id` did not cascade deletes, unlike `snapshot_files` and `snapshot_blobs`. This caused FK violations when deleting snapshots with associated upload records (if FK enforcement is enabled) unless uploads were manually deleted first.

Adds `ON DELETE CASCADE` to the `snapshot_id` FK in `schema.sql` for consistency with the other snapshot-referencing tables.

`docker build .` passes (fmt-check, lint, all tests, build).

closes #18

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #44
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/database/schema.sql

@@ -130,7 +130,7 @@ CREATE TABLE IF NOT EXISTS uploads (
     size INTEGER NOT NULL,
     duration_ms INTEGER NOT NULL,
     FOREIGN KEY (blob_hash) REFERENCES blobs(blob_hash),
-    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id)
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE
 );
 
 -- Index for efficient snapshot lookups