feat: sync agent-browser skill with upstream vercel-labs/agent-browser

Update SKILL.md to match the latest upstream skill from
vercel-labs/agent-browser, adding substantial new capabilities:

- Authentication (auth vault, profiles, session persistence, state files)
- Command chaining, annotated screenshots, diffing
- Security features (content boundaries, domain allowlist, action policy)
- iOS Simulator support, Lightpanda engine, downloads, clipboard
- JS eval improvements (--stdin, -b for shell safety)
- Timeout guidance, config files, session cleanup

Add 7 reference docs (commands, authentication, snapshot-refs,
session-management, video-recording, profiling, proxy-support) and
3 ready-to-use shell templates.

Kept our YAML frontmatter, setup check section, and Playwright MCP
comparison table which are unique to our plugin context.

plugins/compound-engineering/skills/agent-browser/templates/form-automation.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+# Template: Form Automation Workflow
+# Purpose: Fill and submit web forms with validation
+# Usage: ./form-automation.sh <form-url>
+#
+# This template demonstrates the snapshot-interact-verify pattern:
+# 1. Navigate to form
+# 2. Snapshot to get element refs
+# 3. Fill fields using refs
+# 4. Submit and verify result
+#
+# Customize: Update the refs (@e1, @e2, etc.) based on your form's snapshot output
+
+set -euo pipefail
+
+FORM_URL="${1:?Usage: $0 <form-url>}"
+
+echo "Form automation: $FORM_URL"
+
+# Step 1: Navigate to form
+agent-browser open "$FORM_URL"
+agent-browser wait --load networkidle
+
+# Step 2: Snapshot to discover form elements
+echo ""
+echo "Form structure:"
+agent-browser snapshot -i
+
+# Step 3: Fill form fields (customize these refs based on snapshot output)
+#
+# Common field types:
+#   agent-browser fill @e1 "John Doe"           # Text input
+#   agent-browser fill @e2 "user@example.com"   # Email input
+#   agent-browser fill @e3 "SecureP@ss123"      # Password input
+#   agent-browser select @e4 "Option Value"     # Dropdown
+#   agent-browser check @e5                     # Checkbox
+#   agent-browser click @e6                     # Radio button
+#   agent-browser fill @e7 "Multi-line text"   # Textarea
+#   agent-browser upload @e8 /path/to/file.pdf # File upload
+#
+# Uncomment and modify:
+# agent-browser fill @e1 "Test User"
+# agent-browser fill @e2 "test@example.com"
+# agent-browser click @e3  # Submit button
+
+# Step 4: Wait for submission
+# agent-browser wait --load networkidle
+# agent-browser wait --url "**/success"  # Or wait for redirect
+
+# Step 5: Verify result
+echo ""
+echo "Result:"
+agent-browser get url
+agent-browser snapshot -i
+
+# Optional: Capture evidence
+agent-browser screenshot /tmp/form-result.png
+echo "Screenshot saved: /tmp/form-result.png"
+
+# Cleanup
+agent-browser close
+echo "Done"