Complete three-tier config migration (gt-k1lr)

- Add doctor checks for new config architecture:
  - SettingsCheck: Verify rigs have settings/ directory
  - RuntimeGitignoreCheck: Verify .runtime/ is gitignored
  - LegacyGastownCheck: Detect/remove old .gastown/ dirs
- Update .gitignore to include .runtime/
- Update architecture.md with new directory structure
- Update hq.md to clarify PGT vs GGT config locations

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

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

internal/cmd/doctor.go

@@ -70,6 +70,11 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewWispSizeCheck())
 	d.Register(doctor.NewWispStaleCheck())
 
+	// Config architecture checks
+	d.Register(doctor.NewSettingsCheck())
+	d.Register(doctor.NewRuntimeGitignoreCheck())
+	d.Register(doctor.NewLegacyGastownCheck())
+
 	// Run checks
 	var report *doctor.Report
 	if doctorFix {