docs: add AI Traceability & Attribution guide

Comprehensive documentation on AI code attribution and disclosure:

- New guide: guide/ai-traceability.md (~640 lines)
  - LLVM "Human-in-the-Loop" policy (Assisted-by trailer)
  - Ghostty mandatory disclosure pattern
  - Fedora contributor accountability framework
  - git-ai tool documentation
  - PromptPwnd security vulnerability
  - Four-level disclosure spectrum
  - Implementation guides (solo, team, enterprise)

- Templates: examples/config/
  - CONTRIBUTING-ai-disclosure.md
  - PULL_REQUEST_TEMPLATE-ai.md

- Cross-references added to:
  - ultimate-guide.md (after Co-Authored-By section)
  - learning-with-ai.md (after Vibe Coding Trap)
  - security-hardening.md (See Also)
  - guide/README.md (table of contents)

- reference.yaml: 14 new entries for AI traceability topics

Source: Vibe coding needs git blame (Piotr Migdał, Jan 2026)
+ Perplexity research on LLVM, Ghostty, Fedora policies

Co-Authored-By: Claude <noreply@anthropic.com>

guide/README.md

@@ -16,6 +16,7 @@ Core documentation for mastering Claude Code.
 | [observability.md](./observability.md) | Session monitoring and cost tracking | 15 min |
 | [methodologies.md](./methodologies.md) | 15 development methodologies reference (TDD, SDD, BDD, etc.) | 20 min |
 | [security-hardening.md](./security-hardening.md) | Security threats, MCP vetting, injection defense | 25 min |
+| [ai-traceability.md](./ai-traceability.md) | AI attribution, disclosure policies, git-ai, compliance | 20 min |
 | [devops-sre.md](./devops-sre.md) | FIRE framework for infrastructure diagnosis and incident response | 30 min |
 | [ai-ecosystem.md](./ai-ecosystem.md) | Complementary AI tools (Perplexity, Gemini, Kimi, NotebookLM, TTS) | 30 min |
 | [cowork.md](./cowork.md) | Claude Cowork: Summary (see [dedicated repo](https://github.com/FlorianBruniaux/claude-cowork-guide) for full docs) | 5 min |