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/methodologies.md

@@ -132,6 +132,8 @@ Document your team's plan-first triggers:
 
 **See also**: [Plan Mode documentation](./ultimate-guide.md#23-plan-mode) for `/plan` command usage.
 
+> **Advanced pattern**: For an iterative annotation-based approach to plan-driven development, see [Custom Markdown Plans (Boris Tane Pattern)](./workflows/plan-driven.md#advanced-custom-markdown-plans-boris-tane-pattern).
+
 ---
 
 ### Tier 2: Specification & Architecture