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/keepalive/keepalive.go

@@ -17,7 +17,7 @@ type State struct {
 	Timestamp   time.Time `json:"timestamp"`
 }
 
-// Touch updates the keepalive file in the workspace's .gastown directory.
+// Touch updates the keepalive file in the workspace's .runtime directory.
 // It silently ignores errors (best-effort signaling).
 func Touch(command string) {
 	TouchWithArgs(command, nil)
@@ -43,10 +43,10 @@ func TouchWithArgs(command string, args []string) {
 // TouchInWorkspace updates the keepalive file in a specific workspace.
 // It silently ignores errors (best-effort signaling).
 func TouchInWorkspace(workspaceRoot, command string) {
-	gastown := filepath.Join(workspaceRoot, ".gastown")
+	runtimeDir := filepath.Join(workspaceRoot, ".runtime")
 
-	// Ensure .gastown directory exists
-	if err := os.MkdirAll(gastown, 0755); err != nil {
+	// Ensure .runtime directory exists
+	if err := os.MkdirAll(runtimeDir, 0755); err != nil {
 		return
 	}
 
@@ -60,14 +60,14 @@ func TouchInWorkspace(workspaceRoot, command string) {
 		return
 	}
 
-	keepalivePath := filepath.Join(gastown, "keepalive.json")
+	keepalivePath := filepath.Join(runtimeDir, "keepalive.json")
 	_ = os.WriteFile(keepalivePath, data, 0644)
 }
 
 // Read returns the current keepalive state for the workspace.
 // Returns nil if the file doesn't exist or can't be read.
 func Read(workspaceRoot string) *State {
-	keepalivePath := filepath.Join(workspaceRoot, ".gastown", "keepalive.json")
+	keepalivePath := filepath.Join(workspaceRoot, ".runtime", "keepalive.json")
 
 	data, err := os.ReadFile(keepalivePath)
 	if err != nil {

internal/keepalive/keepalive_test.go

@@ -86,12 +86,12 @@ func TestDirectoryCreation(t *testing.T) {
 	tmpDir := t.TempDir()
 	workDir := filepath.Join(tmpDir, "some", "nested", "workspace")
 
-	// Touch should create .gastown directory
+	// Touch should create .runtime directory
 	TouchInWorkspace(workDir, "gt test")
 
 	// Verify directory was created
-	gastown := filepath.Join(workDir, ".gastown")
-	if _, err := os.Stat(gastown); os.IsNotExist(err) {
-		t.Error("expected .gastown directory to be created")
+	runtimeDir := filepath.Join(workDir, ".runtime")
+	if _, err := os.Stat(runtimeDir); os.IsNotExist(err) {
+		t.Error("expected .runtime directory to be created")
 	}
 }