feat(ci): auto-close problem issues when a solution lands in work/

Reconciles work/ against open `problem` issues instead of diffing the push,
so re-runs are no-ops and backfills need no special casing.

Skips scaffolded stubs: `bun run pick` writes a statement header plus an
empty body, so file existence alone must not close an issue.

package.json

@@ -6,6 +6,7 @@
     "dev": "blume dev",
     "build": "blume build",
     "doctor": "blume doctor",
+    "close-solved": "bun scripts/close-solved.ts",
     "pick": "bun scripts/pick.ts",
     "sync": "bun scripts/sync.ts",
     "test": "bun scripts/test.ts"