fix: resolve CI lint errors and Windows test timeout

- Fix gosec G204/G304 warnings by adding exclusions for safe subprocess
  launches and file reads in doctor.go, jira.go, migrate_sync.go, and
  syncbranch/worktree.go
- Fix misspell: "cancelled" -> "canceled" in sync.go
- Fix unparam: mark unused ctx params in jira.go placeholder functions
- Fix errcheck: explicitly ignore fmt.Sscanf return in doctor.go and
  use closure pattern for deferred os.RemoveAll in worktree.go
- Increase Windows test timeout from 10m to 20m to prevent CI timeouts

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

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

cmd/bd/doctor.go

@@ -2515,7 +2515,7 @@ func checkSyncBranchHealth(path string) doctorCheck {
 		fileCount := len(strings.Split(diffFiles, "\n"))
 		// Parse ahead count as int for comparison
 		aheadCountInt := 0
-		fmt.Sscanf(aheadCount, "%d", &aheadCountInt)
+		_, _ = fmt.Sscanf(aheadCount, "%d", &aheadCountInt)
 
 		// Only warn if significantly behind (20+ commits AND 50+ source files)
 		// Small drift is normal between bd sync operations