fix: preserve MCP tool params when MCP schemas are rendered as allOf

[sonwr]

This fixes MCP tool parameter rendering when the schema is valid but represented as allOf after Codebuff combines it with the end-step flag.

What was happening:

• MCP returned a valid input schema
• Codebuff converted the schema and combined it with the end-step flag
• The resulting JSON Schema could be represented as allOf
• paramsSection() only checked top-level properties, so it incorrectly rendered the tool as having no params

What changed:

• Treat schemas with allOf, anyOf, oneOf, or non-empty required as meaningful
• Keep rendering the full JSON Schema instead of falling back to Params: None

How I tested it:

• Reproduced locally with a FastMCP server matching issue MCP dropping all input schemas #450
• Before the fix, the MCP tool description rendered Params: None
• After the fix, the rendered schema includes the expected name parameter
• Added a regression test covering the allOf case

Fixes #450

[jahooma]

Nice, thanks for the fix!