feat: add document title and save tools

[giri256]

Summary

• add set-document-title to rename the selected Draw.io document through its active file provider
• preserve the current .drawio, .drawio.svg, .drawio.png, .xml, .svg, or .png suffix when the requested title omits one
• add save-document to trigger Draw.io's existing File > Save action in the current storage mode
• route and queue both tools through the existing multi-document infrastructure
• document that provider authentication, conflict, or Save As prompts may still require user interaction

The plugin handlers are isolated under src/tools/. They use Draw.io's existing file rename callback and save action; no version-specific implementation was needed for the currently supported compatibility window.

Testing

• drawio-mcp-plugin build
• drawio-mcp-server build
• build/tool-registry.test.js — 19 passed
• focused HTTP MCP tools/list test — passed
• drawio-mcp-server lint (Biome + TypeScript) — passed
• Prettier check for changed TypeScript files — passed

Closes #57

[lgazo]

Thank you