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/wrappers/scripts/gt-codex

@@ -0,0 +1,18 @@
+#!/bin/bash
+# ABOUTME: Wrapper script that runs gt prime before launching codex.
+# ABOUTME: Ensures Gas Town context is available in Codex sessions.
+
+set -e
+
+gastown_enabled() {
+    [[ -n "$GASTOWN_DISABLED" ]] && return 1
+    [[ -n "$GASTOWN_ENABLED" ]] && return 0
+    local state_file="$HOME/.local/state/gastown/state.json"
+    [[ -f "$state_file" ]] && grep -q '"enabled":\s*true' "$state_file" 2>/dev/null
+}
+
+if gastown_enabled && command -v gt &>/dev/null; then
+    gt prime 2>/dev/null || true
+fi
+
+exec codex "$@"

internal/wrappers/scripts/gt-opencode

@@ -0,0 +1,18 @@
+#!/bin/bash
+# ABOUTME: Wrapper script that runs gt prime before launching opencode.
+# ABOUTME: Ensures Gas Town context is available in OpenCode sessions.
+
+set -e
+
+gastown_enabled() {
+    [[ -n "$GASTOWN_DISABLED" ]] && return 1
+    [[ -n "$GASTOWN_ENABLED" ]] && return 0
+    local state_file="$HOME/.local/state/gastown/state.json"
+    [[ -f "$state_file" ]] && grep -q '"enabled":\s*true' "$state_file" 2>/dev/null
+}
+
+if gastown_enabled && command -v gt &>/dev/null; then
+    gt prime 2>/dev/null || true
+fi
+
+exec opencode "$@"

internal/wrappers/wrappers.go

@@ -0,0 +1,68 @@
+// ABOUTME: Manages wrapper scripts for non-Claude agentic coding tools.
+// ABOUTME: Provides gt-codex and gt-opencode wrappers that run gt prime first.
+
+package wrappers
+
+import (
+	"embed"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+//go:embed scripts/*
+var scriptsFS embed.FS
+
+func Install() error {
+	binDir, err := binPath()
+	if err != nil {
+		return fmt.Errorf("determining bin directory: %w", err)
+	}
+
+	if err := os.MkdirAll(binDir, 0755); err != nil {
+		return fmt.Errorf("creating bin directory: %w", err)
+	}
+
+	wrappers := []string{"gt-codex", "gt-opencode"}
+	for _, name := range wrappers {
+		content, err := scriptsFS.ReadFile("scripts/" + name)
+		if err != nil {
+			return fmt.Errorf("reading embedded %s: %w", name, err)
+		}
+
+		destPath := filepath.Join(binDir, name)
+		if err := os.WriteFile(destPath, content, 0755); err != nil {
+			return fmt.Errorf("writing %s: %w", name, err)
+		}
+	}
+
+	return nil
+}
+
+func Remove() error {
+	binDir, err := binPath()
+	if err != nil {
+		return err
+	}
+
+	wrappers := []string{"gt-codex", "gt-opencode"}
+	for _, name := range wrappers {
+		destPath := filepath.Join(binDir, name)
+		os.Remove(destPath)
+	}
+
+	return nil
+}
+
+func binPath() (string, error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, "bin"), nil
+}
+
+func BinDir() string {
+	p, _ := binPath()
+	return p
+}