fix: restore last-touched to gitignore template (GH#838)

The last-touched file was accidentally removed from GitignoreTemplate
in commit 310d374 (GH#814 fix). This restores it and adds it to
requiredPatterns so bd doctor will detect outdated gitignores.

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

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

cmd/bd/doctor/gitignore.go

@@ -22,6 +22,7 @@ daemon.log
 daemon.pid
 bd.sock
 sync-state.json
+last-touched
 
 # Local version tracking (prevents upgrade notification spam after git ops)
 .local_version
@@ -59,6 +60,7 @@ var requiredPatterns = []string{
 	"beads.right.meta.json",
 	"*.db?*",
 	"redirect",
+	"last-touched",
 }
 
 // CheckGitignore checks if .beads/.gitignore is up to date