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/prime.go

@@ -22,6 +22,7 @@ import (
 	"github.com/steveyegge/gastown/internal/lock"
 	"github.com/steveyegge/gastown/internal/rig"
 	"github.com/steveyegge/gastown/internal/session"
+	"github.com/steveyegge/gastown/internal/state"
 	"github.com/steveyegge/gastown/internal/style"
 	"github.com/steveyegge/gastown/internal/templates"
 	"github.com/steveyegge/gastown/internal/workspace"
@@ -81,12 +82,15 @@ func init() {
 type RoleContext = RoleInfo
 
 func runPrime(cmd *cobra.Command, args []string) error {
+	if !state.IsEnabled() {
+		return nil
+	}
+
 	cwd, err := os.Getwd()
 	if err != nil {
 		return fmt.Errorf("getting current directory: %w", err)
 	}
 
-	// Find town root
 	townRoot, err := workspace.FindFromCwd()
 	if err != nil {
 		return fmt.Errorf("finding workspace: %w", err)