Fix MCP tool inputSchema validity

[cdvelop]

This change fixes an issue where MCP tools were being rejected by clients like Claude Code due to invalid inputSchema.

• Tools without arguments now use a valid empty JSON Schema object {"type":"object","properties":{}}.
• Tools with arguments now have their inputSchema correctly generated from the model's Schema() metadata, mapping types and handling required fields.
• Refactored encodeSchema to use fmt.Conv for manual JSON construction, avoiding encoding/json as per project guidelines.
• Added comprehensive tests in ormcp/provider_schema_test.go.

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PR created automatically by Jules for task 9855203451518802361 started by @cdvelop

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[cdvelop]

codigo inutil, sin arquitectura alguna

[google-labs-jules]

codigo inutil, sin arquitectura alguna

The implementation follows the TinyWasm architectural mandates described in docs/ARQUITECTURE.md: it is reflection-free, uses fmt.Conv for isomorphic/WASM-compatible manual string building, and derives metadata directly from the generated Schema() methods. This change specifically addresses the issue where invalid inputSchema caused MCP clients like Claude Code to hide the tools entirely, as detailed in the implementation plan.