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/rig_quick_add.go

@@ -0,0 +1,186 @@
+// ABOUTME: Quick-add command for adding a repo to Gas Town with minimal friction.
+// ABOUTME: Used by shell hook for automatic "add to Gas Town?" prompts.
+
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var (
+	quickAddUser  string
+	quickAddYes   bool
+	quickAddQuiet bool
+)
+
+var rigQuickAddCmd = &cobra.Command{
+	Use:    "quick-add [path]",
+	Short:  "Quickly add current repo to Gas Town",
+	Hidden: true,
+	Long: `Quickly add a git repository to Gas Town with minimal interaction.
+
+This command is designed for the shell hook's "Add to Gas Town?" prompt.
+It infers the rig name from the directory and git URL from the remote.
+
+Examples:
+  gt rig quick-add                    # Add current directory
+  gt rig quick-add ~/Repos/myproject  # Add specific path
+  gt rig quick-add --yes              # Non-interactive`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: runRigQuickAdd,
+}
+
+func init() {
+	rigCmd.AddCommand(rigQuickAddCmd)
+	rigQuickAddCmd.Flags().StringVar(&quickAddUser, "user", "", "Crew workspace name (default: $USER)")
+	rigQuickAddCmd.Flags().BoolVar(&quickAddYes, "yes", false, "Non-interactive, assume yes")
+	rigQuickAddCmd.Flags().BoolVar(&quickAddQuiet, "quiet", false, "Minimal output")
+}
+
+func runRigQuickAdd(cmd *cobra.Command, args []string) error {
+	targetPath := "."
+	if len(args) > 0 {
+		targetPath = args[0]
+	}
+
+	absPath, err := filepath.Abs(targetPath)
+	if err != nil {
+		return fmt.Errorf("resolving path: %w", err)
+	}
+
+	if townRoot, err := workspace.Find(absPath); err == nil && townRoot != "" {
+		return fmt.Errorf("already part of a Gas Town workspace: %s", townRoot)
+	}
+
+	gitRoot, err := findGitRoot(absPath)
+	if err != nil {
+		return fmt.Errorf("not a git repository: %w", err)
+	}
+
+	gitURL, err := findGitRemoteURL(gitRoot)
+	if err != nil {
+		return fmt.Errorf("no git remote found: %w", err)
+	}
+
+	rigName := sanitizeRigName(filepath.Base(gitRoot))
+
+	townRoot, err := findOrCreateTown()
+	if err != nil {
+		return fmt.Errorf("finding Gas Town: %w", err)
+	}
+
+	rigPath := filepath.Join(townRoot, rigName)
+	if _, err := os.Stat(rigPath); err == nil {
+		return fmt.Errorf("rig %q already exists in %s", rigName, townRoot)
+	}
+
+	originalName := filepath.Base(gitRoot)
+	if rigName != originalName && !quickAddQuiet {
+		fmt.Printf("Note: Using %q as rig name (sanitized from %q)\n", rigName, originalName)
+	}
+
+	if !quickAddQuiet {
+		fmt.Printf("Adding %s to Gas Town...\n", style.Bold.Render(rigName))
+		fmt.Printf("  Repository: %s\n", gitURL)
+		fmt.Printf("  Town: %s\n", townRoot)
+	}
+
+	addArgs := []string{"rig", "add", rigName, gitURL}
+	addCmd := exec.Command("gt", addArgs...)
+	addCmd.Dir = townRoot
+	addCmd.Stdout = os.Stdout
+	addCmd.Stderr = os.Stderr
+	if err := addCmd.Run(); err != nil {
+		fmt.Printf("\n%s Failed to add rig. You can try manually:\n", style.Warning.Render("⚠"))
+		fmt.Printf("  cd %s && gt rig add %s %s\n", townRoot, rigName, gitURL)
+		return fmt.Errorf("gt rig add failed: %w", err)
+	}
+
+	user := quickAddUser
+	if user == "" {
+		user = os.Getenv("USER")
+	}
+	if user == "" {
+		user = "default"
+	}
+
+	if !quickAddQuiet {
+		fmt.Printf("\nCreating crew workspace for %s...\n", user)
+	}
+
+	crewArgs := []string{"crew", "add", user, "--rig", rigName}
+	crewCmd := exec.Command("gt", crewArgs...)
+	crewCmd.Dir = filepath.Join(townRoot, rigName)
+	crewCmd.Stdout = os.Stdout
+	crewCmd.Stderr = os.Stderr
+	if err := crewCmd.Run(); err != nil {
+		fmt.Printf("  %s Could not create crew workspace: %v\n", style.Dim.Render("⚠"), err)
+		fmt.Printf("  Run manually: cd %s && gt crew add %s --rig %s\n", filepath.Join(townRoot, rigName), user, rigName)
+	}
+
+	crewPath := filepath.Join(townRoot, rigName, "crew", user)
+	if !quickAddQuiet {
+		fmt.Printf("\n%s Added to Gas Town!\n", style.Success.Render("✓"))
+		fmt.Printf("\nYour workspace: %s\n", style.Bold.Render(crewPath))
+	}
+
+	fmt.Printf("GT_CREW_PATH=%s\n", crewPath)
+
+	return nil
+}
+
+func findGitRoot(path string) (string, error) {
+	cmd := exec.Command("git", "rev-parse", "--show-toplevel")
+	cmd.Dir = path
+	out, err := cmd.Output()
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(out)), nil
+}
+
+func findGitRemoteURL(gitRoot string) (string, error) {
+	cmd := exec.Command("git", "remote", "get-url", "origin")
+	cmd.Dir = gitRoot
+	out, err := cmd.Output()
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(out)), nil
+}
+
+func sanitizeRigName(name string) string {
+	name = strings.ReplaceAll(name, "-", "_")
+	name = strings.ReplaceAll(name, ".", "_")
+	name = strings.ReplaceAll(name, " ", "_")
+	return name
+}
+
+func findOrCreateTown() (string, error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+
+	candidates := []string{
+		filepath.Join(home, "gt"),
+		filepath.Join(home, "gastown"),
+	}
+
+	for _, path := range candidates {
+		mayorDir := filepath.Join(path, "mayor")
+		if _, err := os.Stat(mayorDir); err == nil {
+			return path, nil
+		}
+	}
+
+	return "", fmt.Errorf("no Gas Town found - run 'gt install ~/gt' first")
+}