release: v3.28.1 - Visual Diagrams Series (40 Mermaid diagrams)

guide/diagrams/: new directory with 40 interactive Mermaid diagrams
- 10 thematic files: foundations, context/sessions, configuration,
  architecture, MCP ecosystem, dev workflows, multi-agent patterns,
  security/production, cost/optimization, adoption/learning
- Each diagram: Mermaid (GitHub-native) + ASCII fallback + source link
- Bold Guy palette (6-color system) consistent across all diagrams
- README with index, visual palette legend, navigation by use case

Also includes (backlog from v3.28.0→v3.28.1):
- guide/ultimate-guide.md: Managing Large MCP Server Sets, AI Code
  Disclosure Policy, claude-mem Gemini alternative, observability
- guide/workflows/plan-driven.md: Boris Tane custom markdown plans (+172L)
- guide/security-hardening.md: Part 4 PR security review workflow
- examples/agents/security-patcher.md: new security agent
- examples/hooks/bash/security-gate.sh: PreToolUse security hook
- guide/observability.md: activity monitoring, external tools, proxying
- docs/resource-evaluations/: 4 new evaluations (Boris Cherny, Moigneu,
  Boris Tane, Aristote AI instructions)
- README.md: Visual Diagrams section in "What Makes This Guide Unique"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/skills/pdf-generator.md

@@ -25,6 +25,34 @@ This skill assists with:
 | **Typst** | 0.13.0 | Modern typography (integrated) |
 | **Pandoc** | 3.x | Markdown conversion (integrated) |
 
+### Pipeline de génération
+
+```
+  SOURCE              OUTIL           TEMPLATE              OUTPUT
+  ──────              ─────           ────────              ──────
+
+  .qmd  ──────────► Quarto ────► --to whitepaper-typst ──► Typst 0.13 ──► .pdf ✅
+  (Markdown           │           (_extensions/               (~270K–1.7M,
+  + YAML)             │            typst-template.typ)         stylé)
+                      │
+                      └──────► --to epub ──► Pandoc ──────────────────► .epub
+                                             + epub-styles.css
+
+  ⚠️  --to pdf (sans template) → PDF petit, non stylé → Toujours préférer --to whitepaper-typst
+```
+
+### Formats disponibles
+
+```
+  ┌──────────────────────┬────────────────────────┬──────────────────┐
+  │ Format               │ Commande               │ Sortie           │
+  ├──────────────────────┼────────────────────────┼──────────────────┤
+  │ PDF stylé ✅         │ --to whitepaper-typst  │ ~270K–1.7M       │
+  │ PDF standard ❌      │ --to pdf               │ ~80-190K, brut   │
+  │ EPUB                 │ --to epub              │ epub-output/     │
+  └──────────────────────┴────────────────────────┴──────────────────┘
+```
+
 ## Quick Start
 
 ### Installation