Add configurable title rendering for Mermaid diagrams

[Copilot]

Adds showTitle parameter to control Mermaid frontmatter title rendering across all diagram types (project graphs, ERDs, class diagrams).

Changes

• Renderers: Introduced DiagramOptions record with ShowTitle property passed to Render() methods, replacing mutable state pattern
• CLI: Added --show-title <true|false> option to all visualization commands (defaults to true)
• MCP: Added showTitle parameter to all tool methods (GetProjectGraph, GetErd, GetClassDiagram)

Example

# Suppress title in output
projgraph visualize MySolution.sln --show-title false

# MCP call with title disabled
GetProjectGraph(path: "MySolution.sln", showTitle: false)

The stateless options-as-parameter approach ensures thread safety for singleton-registered renderers in long-lived hosts.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.