feat: Add clone-divergence check to bd doctor (gt-wqck)

Adds CloneDivergenceCheck that detects when git clones have drifted
significantly behind origin/main:
- >10 commits behind: WARNING
- >50 commits behind: ERROR (EMERGENCY)

Only checks clones on main branch, since off-main clones are already
caught by BranchCheck. This distinguishes from beads-sync divergence
which is expected behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/doctor.go

@@ -29,6 +29,10 @@ Cleanup checks (fixable):
   - orphan-processes         Detect orphaned Claude processes
   - wisp-gc                  Detect and clean abandoned wisps (>1h)
 
+Clone divergence checks:
+  - persistent-role-branches Detect crew/witness/refinery not on main
+  - clone-divergence         Detect clones significantly behind origin/main
+
 Patrol checks:
   - patrol-molecules-exist   Verify patrol molecules exist
   - patrol-hooks-wired       Verify daemon triggers patrols
@@ -75,6 +79,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewWispGCCheck())
 	d.Register(doctor.NewBranchCheck())
 	d.Register(doctor.NewBeadsSyncOrphanCheck())
+	d.Register(doctor.NewCloneDivergenceCheck())
 	d.Register(doctor.NewIdentityCollisionCheck())
 	d.Register(doctor.NewLinkedPaneCheck())
 	d.Register(doctor.NewThemeCheck())