feat: Set and Forget - Seamless Gas Town Integration (#255)

Adds shell integration for automatic Gas Town context detection.

Features:
- `gt enable` / `gt disable` - Global on/off switch
- `gt shell install|remove|status` - Shell integration management
- `gt rig quick-add [path]` - One-command project setup
- `gt uninstall` - Clean removal with options
- Shell hook auto-sets GT_TOWN_ROOT/GT_RIG on cd

Implementation:
- XDG-compliant state storage (~/.local/state/gastown/)
- Safe RC file manipulation with block markers
- Environment overrides (GASTOWN_DISABLED/ENABLED)
- Doctor check for global state validation

Co-authored-by: Sohail Mohammad <sohailm25@gmail.com>

internal/cmd/install.go

@@ -16,9 +16,12 @@ import (
 	"github.com/steveyegge/gastown/internal/deps"
 	"github.com/steveyegge/gastown/internal/formula"
 	"github.com/steveyegge/gastown/internal/session"
+	"github.com/steveyegge/gastown/internal/shell"
+	"github.com/steveyegge/gastown/internal/state"
 	"github.com/steveyegge/gastown/internal/style"
 	"github.com/steveyegge/gastown/internal/templates"
 	"github.com/steveyegge/gastown/internal/workspace"
+	"github.com/steveyegge/gastown/internal/wrappers"
 )
 
 var (
@@ -30,6 +33,8 @@ var (
 	installGit        bool
 	installGitHub     string
 	installPublic     bool
+	installShell      bool
+	installWrappers   bool
 )
 
 var installCmd = &cobra.Command{
@@ -55,7 +60,8 @@ Examples:
   gt install ~/gt --no-beads                   # Skip .beads/ initialization
   gt install ~/gt --git                        # Also init git with .gitignore
   gt install ~/gt --github=user/repo           # Create private GitHub repo (default)
-  gt install ~/gt --github=user/repo --public  # Create public GitHub repo`,
+  gt install ~/gt --github=user/repo --public  # Create public GitHub repo
+  gt install ~/gt --shell                      # Install shell integration (sets GT_TOWN_ROOT/GT_RIG)`,
 	Args: cobra.MaximumNArgs(1),
 	RunE: runInstall,
 }
@@ -69,6 +75,8 @@ func init() {
 	installCmd.Flags().BoolVar(&installGit, "git", false, "Initialize git with .gitignore")
 	installCmd.Flags().StringVar(&installGitHub, "github", "", "Create GitHub repo (format: owner/repo, private by default)")
 	installCmd.Flags().BoolVar(&installPublic, "public", false, "Make GitHub repo public (use with --github)")
+	installCmd.Flags().BoolVar(&installShell, "shell", false, "Install shell integration (sets GT_TOWN_ROOT/GT_RIG env vars)")
+	installCmd.Flags().BoolVar(&installWrappers, "wrappers", false, "Install gt-codex/gt-opencode wrapper scripts to ~/bin/")
 	rootCmd.AddCommand(installCmd)
 }
 
@@ -260,6 +268,29 @@ func runInstall(cmd *cobra.Command, args []string) error {
 		fmt.Printf("   ✓ Created .claude/commands/ (slash commands for all agents)\n")
 	}
 
+	if installShell {
+		fmt.Println()
+		if err := shell.Install(); err != nil {
+			fmt.Printf("   %s Could not install shell integration: %v\n", style.Dim.Render("⚠"), err)
+		} else {
+			fmt.Printf("   ✓ Installed shell integration (%s)\n", shell.RCFilePath(shell.DetectShell()))
+		}
+		if err := state.Enable(Version); err != nil {
+			fmt.Printf("   %s Could not enable Gas Town: %v\n", style.Dim.Render("⚠"), err)
+		} else {
+			fmt.Printf("   ✓ Enabled Gas Town globally\n")
+		}
+	}
+
+	if installWrappers {
+		fmt.Println()
+		if err := wrappers.Install(); err != nil {
+			fmt.Printf("   %s Could not install wrapper scripts: %v\n", style.Dim.Render("⚠"), err)
+		} else {
+			fmt.Printf("   ✓ Installed gt-codex and gt-opencode to %s\n", wrappers.BinDir())
+		}
+	}
+
 	fmt.Printf("\n%s HQ created successfully!\n", style.Bold.Render("✓"))
 	fmt.Println()
 	fmt.Println("Next steps:")