feat: add MCP Resources for static project context

[matixan]

Summary

The server exposes only Tools, no MCP Resources. Resources would provide static context without tool invocations:

• `crosspad://architecture` — CLAUDE.md + architecture overview
• `crosspad://registry` — current app-registry.json
• `crosspad://interfaces` — crosspad-core interface list
• `crosspad://hardware` — hardware quick reference

Scope

• Register resources via MCP SDK `server.resource()`
• Read from filesystem on demand (CLAUDE.md files, registry.json)
• Consider resource templates for per-repo context

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