feat: GStack Browser .app bundle — launcher script + build system

- scripts/app/gstack-browser: dual-mode launcher (dev + .app bundle)
- scripts/build-app.sh: compiles binary, bundles Chromium + extension, creates DMG
- Rebrands Chromium plist during build for "GStack Browser" in menu bar
- 389MB .app, 189MB compressed DMG, launches in ~5s

scripts/app/gstack-browser

@@ -0,0 +1,75 @@
+#!/bin/bash
+# GStack Browser launcher — starts browse server + headed Chromium with extension
+#
+# Works in two modes:
+#   1. Inside .app bundle: Contents/MacOS/gstack-browser → Resources are at ../Resources/
+#   2. Dev mode (run directly): uses global gstack install at ~/.claude/skills/gstack/
+#
+# Usage:
+#   open "GStack Browser.app"          # .app bundle mode
+#   scripts/app/gstack-browser         # dev mode (uses global gstack install)
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+# Detect mode: .app bundle or dev
+if [ -d "$SCRIPT_DIR/../Resources" ]; then
+  # .app bundle mode — resources are alongside in the bundle
+  DIR="$(cd "$SCRIPT_DIR/../Resources" && pwd)"
+else
+  # Dev mode — use global gstack install
+  DIR="$HOME/.claude/skills/gstack"
+fi
+
+# Point Playwright at bundled Chromium (only in .app mode)
+if [ -d "$DIR/chromium" ]; then
+  CHROMIUM_APP=$(ls -d "$DIR/chromium/"*.app 2>/dev/null | head -1)
+  if [ -n "$CHROMIUM_APP" ]; then
+    export GSTACK_CHROMIUM_PATH="$CHROMIUM_APP/Contents/MacOS/$(ls "$CHROMIUM_APP/Contents/MacOS/" | head -1)"
+  fi
+fi
+
+# Browse server config
+export BROWSE_PORT=34567
+export BROWSE_HEADED=1
+
+# Extension: bundled first, then global install
+if [ -d "$DIR/extension" ]; then
+  export BROWSE_EXTENSIONS_DIR="$DIR/extension"
+fi
+
+# Server script: bundled source first, then global install
+if [ -f "$DIR/src/server.ts" ]; then
+  export BROWSE_SERVER_SCRIPT="$DIR/src/server.ts"
+elif [ -f "$HOME/.claude/skills/gstack/browse/src/server.ts" ]; then
+  export BROWSE_SERVER_SCRIPT="$HOME/.claude/skills/gstack/browse/src/server.ts"
+fi
+
+# Browse binary: bundled .app first, then global install
+# Note: -x on a directory is true, so check -f (regular file) too
+BROWSE_BIN=""
+for candidate in "$DIR/browse" "$DIR/browse/dist/browse" "$HOME/.claude/skills/gstack/browse/dist/browse"; do
+  if [ -f "$candidate" ] && [ -x "$candidate" ]; then
+    BROWSE_BIN="$candidate"
+    break
+  fi
+done
+
+if [ -z "$BROWSE_BIN" ]; then
+  echo "ERROR: browse binary not found. Run 'bun run build' in the gstack repo or reinstall GStack Browser."
+  exit 1
+fi
+
+# Ensure profile directory
+mkdir -p ~/.gstack/chromium-profile
+
+# Project binding: use last-used project dir, default to home
+PROJECT_DIR=$(cat ~/.gstack/last-project 2>/dev/null || echo "$HOME")
+if [ ! -d "$PROJECT_DIR" ]; then
+  PROJECT_DIR="$HOME"
+fi
+cd "$PROJECT_DIR"
+
+# Launch browse in connect mode
+exec "$BROWSE_BIN" connect "$@"