fix: multiple safety check and sync improvements

- bd-dtm: Changed stderr printing to use SafetyWarnings in worktree.go
- bd-ciu: Fixed non-deterministic output order in formatVanishedIssues
- bd-dmd: Removed duplicate safety check message in sync.go
- bd-k2n: PushSyncBranch now recreates worktree if cleaned up
- bd-c5m: Fixed string(rune()) in tests to use strconv.Itoa
- bd-8uk: Added test for SafetyWarnings population
- bd-1kf: Fixed mergePriority to handle negative priorities
- bd-xo9: Documented sync.require_confirmation_on_mass_delete config

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

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

cmd/bd/sync.go

@@ -400,8 +400,8 @@ Use --merge to merge the sync branch back to main branch.`,
 
 							// bd-4u8: Handle safety check with confirmation requirement
 							if pullResult.SafetyCheckTriggered && !pullResult.Pushed {
+								// bd-dmd: Don't duplicate SafetyCheckDetails - it's already in SafetyWarnings
 								// Prompt for confirmation
-								fmt.Fprintf(os.Stderr, "\n⚠️  Mass deletion detected: %s\n", pullResult.SafetyCheckDetails)
 								fmt.Fprintf(os.Stderr, "Push these changes to remote? [y/N]: ")
 
 								var response string