Schema caching with 24hr TTL

[rodaddy]

Cache tool schemas locally to avoid MCP introspection on every CLI call.

• Cache location: ~/.cache/mcp2cli/schemas/.json
• TTL: 24 hours (configurable via MCP2CLI_SCHEMA_TTL)
• Invalidation: manual via mcp2cli cache clear or automatic on TTL expiry
• Foundation for drift detection and auto-regeneration

Requirement: ADV-01