docs(hooks): add JavaScript handler type documentation

[bclermont]

Summary

Added comprehensive documentation for the JavaScript/script handler type in GoClaw hooks system — a previously undocumented feature that executes sandboxed ES5.1 JavaScript for real-time event interception and transformation.

Changes

• New doc: advanced/hooks-javascript.md (349 lines)

  • Handler signature and API
  • Event payload structures per event type
  • 4 practical examples (command blocking, PII redaction, auditing, rate limiting)
  • ES5.1 runtime capabilities and limitations
  • Safety limits (32 KiB source, 4 KiB stdout, concurrency caps, circuit breaker)
  • Matcher/filtering for performance optimization
  • Configuration via WebSocket and Web UI
  • Testing guide
  • Troubleshooting table
  • Best practices

• Updated: advanced/hooks-quality-gates.md

  • Added script handler to the handler types table with link to new doc

• Updated triple-sync (README.md, js/docs-app.js, index.html)

  • Added JavaScript Hooks entry in Advanced section
  • Added DOC_MAP entry with EN/VI/ZH titles
  • Added sidebar link

Test Plan

• Documentation follows existing style and tone
• Triple-sync completed (README, docs-app.js, index.html all updated)
• Examples are ES5.1 compliant and tested against actual code
• Cross-references to hooks-quality-gates.md work
• No orphaned links (all 4 files synchronized)

Context

The script handler (handler_type: "script") is fully implemented in GoClaw (internal/hooks/handlers/script.go, internal/hooks/handlers/script_sandbox.go) but had no user documentation. This PR fills that gap with a complete guide.

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