docs: add AI Chat Showcase — public technical writeup for GitHub

doc/29-AI-CHAT-SHOWCASE.md: comprehensive technical showcase covering
the AI-powered CV navigation feature for potential clients/employers.

9 technical decisions explained with code:
1. ADK Go 1.0 as agent framework
2. Single agent, single tool design
3. Cross-section search across all CV data
4. CV navigation links (GPS for the CV)
5. Dual-provider with auto-fallback (Gemini→Ollama)
6. Model warmup on chat open
7. HTMX + plain JS (no SPA framework)
8. Rate limiting (30 req/hour/IP)
9. Graceful degradation

Linked from README.md and doc index.

doc/00-GO-DOCUMENTATION-INDEX.md

@@ -36,7 +36,7 @@ This documentation covers the core Go systems that power the CV site, with a foc
    - Coverage gap explanations
    - Best practices and CI/CD integration
 
-5. **[AI Chat Agent — CV Assistant Mascot](28-AI-CHAT-AGENT.md)** (~500 lines)
+5. **[AI Chat Agent — CV Assistant Mascot](28-AI-CHAT-AGENT.md)** (~544 lines)
    - Complete mascot feature reference: architecture, components, intelligence
    - ADK Go 1.0 integration with Gemini 2.5 Flash
    - Agent definition with query_cv tool (11 section types, cross-section search)
@@ -47,6 +47,14 @@ This documentation covers the core Go systems that power the CV site, with a foc
    - Design system integration (CSS tokens, dark theme, responsive)
    - Graceful degradation, security, and testing (46 Playwright assertions)
 
+6. **[AI Chat Showcase — Technical Writeup](29-AI-CHAT-SHOWCASE.md)** (~250 lines)
+   - Public-facing technical showcase of the AI chat feature
+   - Architecture diagram with dual-provider fallback
+   - 9 key technical decisions explained with code examples
+   - CV navigation links (GPS for the CV)
+   - Technology stack and file structure
+   - What this demonstrates for potential employers/clients
+
 ## Quick Navigation
 
 ### By Feature