Add Playwright subprocess bridge for real browser automation

Node.js Bridge:
- playwright_bridge.js: JSON-RPC server for Playwright
- fingerprint.js: FIREBIRD fingerprint protection module
- package.json: NPM configuration
- PROTOCOL.md: Full JSON-RPC protocol documentation

Zig Subprocess Spawner:
- subprocess_bridge.zig: Spawns Node.js, communicates via JSON-RPC
- Mock mode fallback when Node.js unavailable
- Fingerprint evolution (0.85 → 0.95)

Test Results:
- All 19 unit tests passing
- Subprocess bridge: 4/4 tests pass (mock mode)
- Framework ready for real browser integration

Files: 6 new, ~1035 lines

Co-authored-by: Ona <no-reply@ona.com>

Author: gHashTag

webarena_agent/bridge/PROTOCOL.md

@@ -0,0 +1,359 @@
+# FIREBIRD Playwright Bridge Protocol
+
+**Version**: 1.0.0  
+**Transport**: JSON-RPC 2.0 over stdin/stdout  
+**Formula**: φ² + 1/φ² = 3 = TRINITY
+
+---
+
+## Overview
+
+The FIREBIRD Playwright Bridge uses JSON-RPC 2.0 for communication between the Zig agent and Node.js Playwright process.
+
+```
+┌─────────────────┐     stdin (JSON-RPC)      ┌─────────────────┐
+│   Zig Agent     │ ─────────────────────────▶│  Node.js Bridge │
+│  (subprocess    │                           │  (Playwright)   │
+│   spawner)      │ ◀───────────────────────── │                 │
+└─────────────────┘     stdout (JSON-RPC)     └─────────────────┘
+```
+
+---
+
+## Request Format
+
+```json
+{
+    "jsonrpc": "2.0",
+    "id": 1,
+    "method": "methodName",
+    "params": { ... }
+}
+```
+
+## Response Format
+
+```json
+{
+    "jsonrpc": "2.0",
+    "id": 1,
+    "result": { ... }
+}
+```
+
+## Error Format
+
+```json
+{
+    "jsonrpc": "2.0",
+    "id": 1,
+    "error": {
+        "code": -32000,
+        "message": "Error description"
+    }
+}
+```
+
+---
+
+## Methods
+
+### connect
+
+Start browser and create context with optional stealth.
+
+**Request:**
+```json
+{
+    "method": "connect",
+    "params": {
+        "headless": true,
+        "viewport": { "width": 1280, "height": 720 },
+        "stealth": true
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "success": true,
+        "mock": false,
+        "sessionId": "session-1234567890",
+        "viewport": { "width": 1280, "height": 720 }
+    }
+}
+```
+
+### disconnect
+
+Close browser and cleanup.
+
+**Request:**
+```json
+{
+    "method": "disconnect"
+}
+```
+
+**Response:**
+```json
+{
+    "result": { "success": true }
+}
+```
+
+### navigate
+
+Navigate to URL.
+
+**Request:**
+```json
+{
+    "method": "navigate",
+    "params": {
+        "url": "https://example.com",
+        "timeout": 30000
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "success": true,
+        "url": "https://example.com/",
+        "title": "Example Domain"
+    }
+}
+```
+
+### click
+
+Click element by selector, ID, or coordinates.
+
+**Request:**
+```json
+{
+    "method": "click",
+    "params": {
+        "selector": "button.submit",
+        "elementId": 42,
+        "coords": { "x": 100, "y": 200 },
+        "timeout": 5000
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": { "success": true }
+}
+```
+
+### type
+
+Type text into element.
+
+**Request:**
+```json
+{
+    "method": "type",
+    "params": {
+        "selector": "input[name='search']",
+        "text": "search query",
+        "delay": 50
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": { "success": true }
+}
+```
+
+### scroll
+
+Scroll page.
+
+**Request:**
+```json
+{
+    "method": "scroll",
+    "params": {
+        "direction": "down",
+        "amount": 300
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": { "success": true }
+}
+```
+
+### getState
+
+Get current page state.
+
+**Request:**
+```json
+{
+    "method": "getState"
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "url": "https://example.com/",
+        "title": "Example Domain",
+        "elementsCount": 42
+    }
+}
+```
+
+### getAccessibilityTree
+
+Get simplified accessibility tree.
+
+**Request:**
+```json
+{
+    "method": "getAccessibilityTree"
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "tree": [
+            {
+                "id": 0,
+                "tag": "button",
+                "role": "button",
+                "text": "Submit",
+                "bounds": { "x": 100, "y": 200, "width": 80, "height": 30 },
+                "clickable": true,
+                "focusable": true
+            }
+        ]
+    }
+}
+```
+
+### screenshot
+
+Take screenshot.
+
+**Request:**
+```json
+{
+    "method": "screenshot",
+    "params": {
+        "format": "base64",
+        "fullPage": false
+    }
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "data": "iVBORw0KGgoAAAANSUhEUgAA...",
+        "format": "png"
+    }
+}
+```
+
+### injectFingerprint
+
+Inject FIREBIRD fingerprint protection.
+
+**Request:**
+```json
+{
+    "method": "injectFingerprint"
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "success": true,
+        "fingerprint": {
+            "canvasNoise": 0.0001,
+            "webglVendor": "Intel Inc.",
+            "webglRenderer": "Intel Iris OpenGL Engine"
+        }
+    }
+}
+```
+
+### ping
+
+Check connection.
+
+**Request:**
+```json
+{
+    "method": "ping"
+}
+```
+
+**Response:**
+```json
+{
+    "result": {
+        "pong": true,
+        "timestamp": 1234567890
+    }
+}
+```
+
+---
+
+## Error Codes
+
+| Code | Message | Description |
+|------|---------|-------------|
+| -32700 | Parse error | Invalid JSON |
+| -32600 | Invalid request | Missing required fields |
+| -32601 | Method not found | Unknown method |
+| -32000 | Server error | Browser/Playwright error |
+
+---
+
+## Mock Mode
+
+When Playwright is not installed, the bridge runs in mock mode:
+- All methods return `{ "success": true, "mock": true }`
+- No actual browser is spawned
+- Useful for testing without dependencies
+
+---
+
+## FIREBIRD Fingerprint Protection
+
+When `stealth: true` is passed to `connect`, the following protections are injected:
+
+1. **Canvas Fingerprint**: Random noise added to canvas data
+2. **WebGL Fingerprint**: Vendor/renderer spoofed
+3. **Audio Fingerprint**: Noise added to audio context
+4. **Navigator Properties**: Platform, hardware info spoofed
+5. **Screen Properties**: Resolution normalized
+
+---
+
+**φ² + 1/φ² = 3 = TRINITY | FIREBIRD BRIDGE PROTOCOL**