fix(install): remove vestigial rigs/ directory creation

The rigs/ directory was created by gt install but never used by
gt rig add, which puts rigs at the town root. Rather than restructure
the entire codebase to use rigs/, we remove the unused directory.

Flat structure is fine - similar to Android top-level layout with
100+ subprojects. Rigs at root works well and avoids a breaking change.

Closes #74

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

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

internal/cmd/gitinit.go

@@ -90,11 +90,6 @@ const HQGitignore = `# Gas Town HQ .gitignore
 # Add rig-specific symlinks here, e.g.:
 # gastown/.beads
 
-# =============================================================================
-# Rigs directory (clones created by 'gt rig add')
-# =============================================================================
-/rigs/*/
-
 # =============================================================================
 # OS and editor files
 # =============================================================================

internal/cmd/install.go

@@ -39,7 +39,6 @@ The HQ (headquarters) is the top-level directory where Gas Town is installed -
 the root of your workspace where all rigs and agents live. It contains:
   - CLAUDE.md            Mayor role context (Mayor runs from HQ root)
   - mayor/               Mayor config, state, and rig registry
-  - rigs/                Managed rig containers (created by 'gt rig add')
   - .beads/              Town-level beads DB (hq-* prefix for mayor mail)
 
 If path is omitted, uses the current directory.
@@ -170,13 +169,6 @@ func runInstall(cmd *cobra.Command, args []string) error {
 	}
 	fmt.Printf("   ✓ Created mayor/rigs.json\n")
 
-	// Create rigs directory (for managed rig clones)
-	rigsDir := filepath.Join(absPath, "rigs")
-	if err := os.MkdirAll(rigsDir, 0755); err != nil {
-		return fmt.Errorf("creating rigs directory: %w", err)
-	}
-	fmt.Printf("   ✓ Created rigs/\n")
-
 	// Create mayor state.json
 	mayorState := &config.AgentState{
 		Role:       "mayor",

internal/cmd/install_integration_test.go

@@ -33,7 +33,6 @@ func TestInstallCreatesCorrectStructure(t *testing.T) {
 	// Verify directory structure
 	assertDirExists(t, hqPath, "HQ root")
 	assertDirExists(t, filepath.Join(hqPath, "mayor"), "mayor/")
-	assertDirExists(t, filepath.Join(hqPath, "rigs"), "rigs/")
 
 	// Verify mayor/town.json
 	townPath := filepath.Join(hqPath, "mayor", "town.json")