Rewrite extension-template-sync to detect unsynced PRs and create issues

Switch from creating sync PRs to opening issues for each unsynced template
PR. The workflow now runs daily-only (no manual dispatch), checks the last
50 merged template PRs by comparing file contents, and creates an issue
with title, summary, differing files, suggested fix, and source PR link.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: edvilme

.github/aw/actions-lock.json

@@ -19,6 +19,11 @@
       "repo": "github/gh-aw/actions/setup",
       "version": "v0.47.5",
       "sha": "9450254bc994da0d6a346ce438a4b3764f01c456"
+    },
+    "github/gh-aw/actions/setup@v0.51.6": {
+      "repo": "github/gh-aw/actions/setup",
+      "version": "v0.51.6",
+      "sha": "33cd6c7f1fee588654ef19def2e6a4174be66197"
     }
   }
 }