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>

internal/syncbranch/worktree.go

@@ -473,7 +473,7 @@ func performContentMerge(ctx context.Context, worktreePath, branch, remote, json
 	if err != nil {
 		return nil, fmt.Errorf("failed to create temp dir: %w", err)
 	}
-	defer os.RemoveAll(tmpDir)
+	defer func() { _ = os.RemoveAll(tmpDir) }()
 
 	baseFile := filepath.Join(tmpDir, "base.jsonl")
 	localFile := filepath.Join(tmpDir, "local.jsonl")