feat(engineering): add browser-automation and spec-driven-workflow skills

browser-automation (564-line SKILL.md, 3 scripts, 3 references):
- Web scraping, form filling, screenshot capture, data extraction
- Anti-detection patterns, cookie/session management, dynamic content
- scraping_toolkit.py, form_automation_builder.py, anti_detection_checker.py
- NOT testing (that's playwright-pro) — this is automation & scraping

spec-driven-workflow (586-line SKILL.md, 3 scripts, 3 references):
- Spec-first development: write spec BEFORE code
- Bounded autonomy rules, 6-phase workflow, self-review checklist
- spec_generator.py, spec_validator.py, test_extractor.py
- Pairs with tdd-guide for red-green-refactor after spec

Updated engineering plugin.json (31 → 33 skills).
Added both to mkdocs.yml nav and generated docs pages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

engineering/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "engineering-advanced-skills",
-  "description": "31 advanced engineering skills: agent designer, agent workflow designer, AgentHub, RAG architect, database designer, migration architect, observability designer, dependency auditor, release manager, API reviewer, CI/CD pipeline builder, MCP server builder, skill security auditor, performance profiler, Helm chart builder, Terraform patterns, focused-fix, and more. Agent skill and plugin for Claude Code, Codex, Gemini CLI, Cursor, OpenClaw.",
+  "description": "33 advanced engineering skills: agent designer, agent workflow designer, AgentHub, RAG architect, database designer, migration architect, observability designer, dependency auditor, release manager, API reviewer, CI/CD pipeline builder, MCP server builder, skill security auditor, performance profiler, Helm chart builder, Terraform patterns, focused-fix, browser-automation, spec-driven-workflow, and more. Agent skill and plugin for Claude Code, Codex, Gemini CLI, Cursor, OpenClaw.",
   "version": "2.1.2",
   "author": {
     "name": "Alireza Rezvani",