Implement three-tier config architecture (gt-k1lr tasks 1-5)

**Architecture changes:**
- Renamed `.gastown/` → `.runtime/` for runtime state (gitignored)
- Added `settings/` directory for rig behavioral config (git-tracked)
- Added `mayor/config.json` for town-level config (MayorConfig type)
- Separated RigConfig (identity) from RigSettings (behavioral)

**File location changes:**
- Town runtime: `~/.gastown/*` → `~/.runtime/*`
- Rig runtime: `<rig>/.gastown/*` → `<rig>/.runtime/*`
- Rig config: `<rig>/.gastown/config.json` → `<rig>/settings/config.json`
- Namepool state: `namepool.json` → `namepool-state.json`

**New types:**
- MayorConfig: town-level behavioral config
- RigSettings: rig behavioral config (merge_queue, theme, namepool)
- RigConfig now identity-only (name, git_url, beads, created_at)

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

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

internal/polecat/manager.go

@@ -48,19 +48,19 @@ func NewManager(r *rig.Rig, g *git.Git) *Manager {
 	// Use the rig root for beads operations (rig-level beads at .beads/)
 	rigPath := r.Path
 
-	// Try to load rig config for namepool settings
-	rigConfigPath := filepath.Join(r.Path, ".gastown", "config.json")
+	// Try to load rig settings for namepool config
+	settingsPath := filepath.Join(r.Path, "settings", "config.json")
 	var pool *NamePool
 
-	rigConfig, err := config.LoadRigConfig(rigConfigPath)
-	if err == nil && rigConfig.Namepool != nil {
+	settings, err := config.LoadRigSettings(settingsPath)
+	if err == nil && settings.Namepool != nil {
 		// Use configured namepool settings
 		pool = NewNamePoolWithConfig(
 			r.Path,
 			r.Name,
-			rigConfig.Namepool.Style,
-			rigConfig.Namepool.Names,
-			rigConfig.Namepool.MaxBeforeNumbering,
+			settings.Namepool.Style,
+			settings.Namepool.Names,
+			settings.Namepool.MaxBeforeNumbering,
 		)
 	} else {
 		// Use defaults