feat(skills): Add hierarchical structure with references and templates (#157)

* feat(skills): Add hierarchical structure with references and templates

Adds modular documentation and executable templates to the agent-browser skill
for better AI agent consumption and progressive disclosure.

## Added

### References (deep-dive documentation)
- `references/snapshot-refs.md` - Ref lifecycle, invalidation, troubleshooting
- `references/session-management.md` - Parallel sessions, state persistence
- `references/authentication.md` - Login flows, OAuth, 2FA patterns
- `references/video-recording.md` - Recording for debugging/docs
- `references/proxy-support.md` - Proxy configuration, geo-testing

### Templates (ready-to-use workflows)
- `templates/form-automation.sh` - Form filling with validation
- `templates/authenticated-session.sh` - Login once, reuse state
- `templates/capture-workflow.sh` - Content extraction with screenshots

## Modified
- `SKILL.md` - Added reference tables linking to new documentation

## Benefits
- Progressive disclosure: Load overview first, deep dives on demand
- Reduced context: Smaller chunks for better LLM token efficiency
- Ready workflows: Copy-paste templates for common patterns

* fix(templates): Make authenticated-session.sh runnable out-of-box

Addresses review feedback: login actions were commented but verification
wasn't, causing script to fail when run as-is.

New approach:
- DISCOVERY MODE runs first (shows form structure)
- LOGIN FLOW section is fully commented as a unit
- User runs once to see refs, then customizes

┌─────────────────────────────────────────────────────────────┐
│ LOGIN FORM STRUCTURE                                        │
├─────────────────────────────────────────────────────────────┤
│ @e1 [input type="email"]                                    │
│ @e2 [input type="password"]                                 │
│ @e3 [button] "Sign In"                                      │
└─────────────────────────────────────────────────────────────┘

skills/agent-browser/templates/form-automation.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+# Template: Form Automation Workflow
+# Fills and submits web forms with validation
+
+set -euo pipefail
+
+FORM_URL="${1:?Usage: $0 <form-url>}"
+
+echo "Automating form at: $FORM_URL"
+
+# Navigate to form page
+agent-browser open "$FORM_URL"
+agent-browser wait --load networkidle
+
+# Get interactive snapshot to identify form fields
+echo "Analyzing form structure..."
+agent-browser snapshot -i
+
+# Example: Fill common form fields
+# Uncomment and modify refs based on snapshot output
+
+# Text inputs
+# agent-browser fill @e1 "John Doe"           # Name field
+# agent-browser fill @e2 "user@example.com"   # Email field
+# agent-browser fill @e3 "+1-555-123-4567"    # Phone field
+
+# Password fields
+# agent-browser fill @e4 "SecureP@ssw0rd!"
+
+# Dropdowns
+# agent-browser select @e5 "Option Value"
+
+# Checkboxes
+# agent-browser check @e6                      # Check
+# agent-browser uncheck @e7                    # Uncheck
+
+# Radio buttons
+# agent-browser click @e8                      # Select radio option
+
+# Text areas
+# agent-browser fill @e9 "Multi-line text content here"
+
+# File uploads
+# agent-browser upload @e10 /path/to/file.pdf
+
+# Submit form
+# agent-browser click @e11                     # Submit button
+
+# Wait for response
+# agent-browser wait --load networkidle
+# agent-browser wait --url "**/success"        # Or wait for redirect
+
+# Verify submission
+echo "Form submission result:"
+agent-browser get url
+agent-browser snapshot -i
+
+# Take screenshot of result
+agent-browser screenshot /tmp/form-result.png
+
+# Cleanup
+agent-browser close
+
+echo "Form automation complete"