review(mirror): init phase-namespaced files + pre-flight snapshot @00:18Z

Cold-verified mirror state, live bridge POLL_REPOS, tests/ dirs.
Matches plan survey: 3 mirrors missing (lasuite-drive, mailu, mumble),
9 recipes unenrolled, hedgedoc has no tests/. Awaiting Builder claims.

machine-docs/BACKLOG-mirror.md

@@ -0,0 +1,10 @@
+# BACKLOG — cc-ci mirror+enroll phase
+
+## Build backlog
+
+(Builder-owned section — read-only for Adversary)
+
+## Adversary findings
+
+(none yet)
+