[FEATURE] `get_architecture` — single-call codebase overview for agents

[Wolfvin]

Problem

When an agent starts a new session on an unfamiliar codebase, it currently needs to:

1. scan the workspace
2. list all files
3. detect frameworks
4. Read several entry point files manually

This costs 10-20k tokens just for orientation.

Proposed Change

Add a get_architecture MCP tool that returns a structured summary in one call:

{
  "languages": {"python": 342, "typescript": 89},
  "frameworks": ["fastapi", "react"],
  "entry_points": ["src/main.py", "src/server.ts"],
  "packages": ["src/api", "src/models", "src/services"],
  "routes": [{"method": "GET", "path": "/users", "handler": "get_users"}],
  "hotspots": ["src/models/user.py (47 dependents)"],
  "total_symbols": 1842,
  "adrs": []  // if ADR feature implemented
}

Why This Matters

An agent that calls get_architecture first has enough context to ask precise questions instead of exploring blindly. Target: orientation in 1 tool call, <1k tokens output.