feat: Add rebrand CI/CD workflows to main branch

- Add 72 rebrand workflow files (polkadot→pezkuwi, substrate→bizinikiwi, cumulus→pezcumulus)
- Add GitHub actions, issue templates, and configs
- Removed unnecessary workflows (fork-sync, gitspiegel, upstream-tracker, sync-templates, backport)
- Renamed zombienet test files to match new naming convention

.github/workflows/reusable-disk-cleanup.yml

@@ -0,0 +1,12 @@
+name: Reusable Disk Cleanup
+
+on:
+  workflow_call:
+
+jobs:
+  # This is a no-op job that other workflows can use to trigger disk cleanup
+  # The actual cleanup happens via the composite action
+  placeholder:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "Disk cleanup is handled by the composite action"