doctor: check and repair the v1.1 committed-read mirror

Read paths use the v1.1 mirror as-is (no read-time self-repair), so a missing, stale, or diverged refs/entire/checkpoints/v1.1 silently makes v1.1 reads miss checkpoints with no repair path. Make doctor the repair tool:

• strategy.DiagnoseCommittedMetadataMirror classifies the mirror against the local v1 tip (read-only): not configured, ok, missing, behind, diverged, or v1-branch-missing.
• entire doctor reports the state and repairs missing/stale/diverged with confirmation (auto under --force) via the existing MirrorCommittedMetadataRef. The mirror-outlives-v1 anomaly is warn-only with a fetch suggestion; restoring v1 is out of scope.
• entire doctor bundle captures entire-related refs plus the mirror diagnosis in entire-refs.txt for bug reports.