feat: add Google Chat bridge for forever mode

- Minimal Express bridge that receives Google Chat webhooks, forwards
  to the forever agent's external listener via JSON-RPC, and pushes
  responses back via Chat API
- Chat API client for async message delivery (Google Chat webhooks
  have a 30s timeout, agent responses take longer)
- JWT verification for Google Chat requests (skippable for local dev)
- External listener default port changed to 3100 (configurable via
  A2A_PORT env var), blocking timeout increased to 30min
- Startup script (scripts/start-forever.sh) launches both processes
- FOREVER.md with full setup instructions (local dev + GCE VM)

scripts/start-forever.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+# Start the forever agent + chat bridge together.
+# Usage: ./scripts/start-forever.sh
+#
+# Required env vars:
+#   GOOGLE_API_KEY          - Gemini API key
+#   GOOGLE_APPLICATION_CREDENTIALS - path to service account key (for Chat API)
+#
+# Optional env vars:
+#   A2A_PORT                - external listener port (default: 3100)
+#   BRIDGE_PORT             - chat bridge port (default: 8081)
+#   CHAT_PROJECT_NUMBER     - Google Cloud project number (for JWT verification)
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+# Default ports
+export A2A_PORT="${A2A_PORT:-3100}"
+export BRIDGE_PORT="${BRIDGE_PORT:-8081}"
+export A2A_URL="${A2A_URL:-http://127.0.0.1:${A2A_PORT}}"
+
+echo "=== Gemini CLI Forever Agent ==="
+echo "Agent listener: localhost:${A2A_PORT}"
+echo "Chat bridge:    0.0.0.0:${BRIDGE_PORT}"
+echo ""
+
+# Build if needed
+if [ ! -d "$REPO_ROOT/packages/a2a-server/dist" ]; then
+  echo "Building a2a-server..."
+  cd "$REPO_ROOT" && npm run build --workspace=packages/a2a-server
+fi
+
+# Start the chat bridge in the background
+echo "Starting chat bridge..."
+node "$REPO_ROOT/packages/a2a-server/dist/src/chat-bridge/bridge.js" &
+BRIDGE_PID=$!
+
+# Cleanup on exit
+cleanup() {
+  echo "Shutting down..."
+  kill "$BRIDGE_PID" 2>/dev/null || true
+  wait "$BRIDGE_PID" 2>/dev/null || true
+}
+trap cleanup EXIT INT TERM
+
+# Start the forever agent in the foreground
+echo "Starting forever agent..."
+cd "$REPO_ROOT"
+npx gemini --forever --a2a-port "$A2A_PORT" --yolo
+
+# If the agent exits, cleanup will fire