docs: add Myths vs Reality appendix + TeammateTool documentation

- Appendix D: Myths vs Reality
  - Myth: Hidden features with secret flags
  - Myth: Tasks API = autonomous agents
  - Myth: 100x faster claims
  - Reality: Documented strengths of Claude Code
  - How to spot reliable vs unreliable sources

- New: TeammateTool experimental feature documentation
  - Multi-agent orchestration capabilities
  - Execution backends (in-process, tmux, iTerm2)
  - Usage patterns (parallel specialists, swarm)
  - Clear warnings about experimental status
  - Community sources cited

- Cheatsheet: Features Méconnues (But Official!) section
  - Tasks API, Background Agents, TeammateTool
  - Session Forking, LSP Tool
  - Pro tip: Read the CHANGELOG

- Reference.yaml: Added line numbers for new sections

- Resource evaluation: Rejected low-quality social media post
  (docs/resource-evaluations/2026-01-27-claude-code-hidden-feature-social-post.md)

Addresses community misinformation while documenting real experimental features with proper sourcing.

guide/cheatsheet.md

@@ -60,6 +60,20 @@
 
 ---
 
+## Features Méconnues (But Official!)
+
+| Feature | Since | What It Does |
+|---------|-------|--------------|
+| **Tasks API** | v2.1.16 | Persistent task lists with dependencies |
+| **Background Agents** | v2.0.60 | Sub-agents work while you code |
+| **TeammateTool** | Experimental | Multi-agent coordination (unstable) |
+| **Session Forking** | v2.1.19 | Rewind + create parallel timeline |
+| **LSP Tool** | v2.0.74 | Code intelligence (go-to-def, refs) |
+
+**Pro tip**: These aren't "secrets"—they're in the [CHANGELOG](https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md). Read it!
+
+---
+
 ## Permission Modes
 
 | Mode | Editing | Execution |