fix(rules): bound structured history inputs

[Hiro-Chiba]

What

This is a small fix for structured tool inputs bypassing enforceTdd's existing maxContentChars history limit.

trimHistory now formats a structured input once and applies the same head-and-tail clipping used for prompts and tool output. Inputs already within the limit keep their original value and object identity.

Does applying the existing per-field limit to tool input match the intended meaning of maxContentChars?

Why

The option bounded prompt text and action output, but an Edit or Write input containing a large file body was still serialized in full when the recent history block was built.

In a local check, a structured input whose JSON representation was 150,014 characters produced a complete 7,909-character validator prompt with maxContentChars: 1000 and retained the explicit truncation marker.

Verification

• npm run checks
• 58 test suites passed
• 539 tests passed, with 26 existing skips
• Prompt-level regression test for a large structured Edit input
• Unit coverage for structured input JSON formatting and clipping