chore: gitignore local pwned-deps cache + drop accidentally-committed sqlite

The capture_demos.py script writes an OSV cache to .pwned-deps-cache/
which got picked up by 'git add -A' in the previous commit. Untrack
it and add an ignore rule so future runs don't re-add it.

Author: claude

.gitignore

@@ -45,3 +45,6 @@ Thumbs.db
 
 # Captured base-image digest (regenerated by `make pin-base`)
 base-image.lock
+
+# pwned-deps local cache
+.pwned-deps-cache/