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>

guide/workflows/pdf-generation.md

@@ -92,6 +92,54 @@ quarto preview document.qmd  # Hot-reload
 └─────────────────────────────────────────────────┘
 ```
 
+### Output Formats & Commands
+
+```
+  FORMAT                COMMANDE                      SORTIE
+  ──────                ────────                      ──────
+
+  PDF standard    →  quarto render doc.qmd            doc.pdf
+                     --to typst                       (sans template custom)
+
+  PDF stylé ✅    →  quarto render doc.qmd            doc.pdf
+                     --to whitepaper-typst            (~270K–1.7M, Bold Guy)
+                     (format custom via _extensions/)
+
+  EPUB            →  quarto render doc.qmd            doc.epub
+                     --to epub
+
+  Preview         →  quarto preview doc.qmd           hot-reload navigateur
+```
+
+### Extension Structure
+
+```
+  _extensions/
+  └── whitepaper/
+      ├── _extension.yml       ← déclare le format "whitepaper-typst"
+      ├── typst-template.typ   ← design system (couleurs, typo, callouts)
+      └── typst-show.typ       ← bridge Quarto → Typst
+
+  ⚠️  Si tu maintiens des copies dans fr/ en/ et racine :
+      garder les 3 fichiers typst-template.typ synchronisés
+```
+
+### Troubleshooting Rapide
+
+```
+  SYMPTÔME                        CAUSE                    FIX
+  ────────                        ─────                    ───
+  PDF petit (~80-190K), non stylé  --to pdf au lieu de      Utiliser --to whitepaper-typst
+                                   --to whitepaper-typst
+
+  Erreur "bibliography"            @ref dans titre callout   Supprimer le @ du titre
+                                   → interprété comme cit.
+
+  Table rendue comme code          Backtick ``` non fermé    Compter les ``` (doit être pair)
+
+  "Extension not found"            Mauvais répertoire        Vérifier _extensions/ path
+```
+
 | Component | Version | Role |
 |-----------|---------|------|
 | **Quarto** | ≥1.4.0 | Orchestration, extensions, multi-format |