fix(tool): parse special filenames in code search

[jxnclty]

Description

Fixes code_search parsing for filenames containing colons and other special characters.

git grep output was parsed using delimiter-sensitive text output, which could cause characters in filenames to be interpreted as part of the match metadata. Binary match notices could also interfere with result parsing and matching-file counts.

This change:

• uses NUL-delimited git grep output so filenames can be parsed without relying on special characters as separators;
• ignores binary files when collecting text search results, preventing binary match notices from corrupting the parsed records;
• preserves support for non-ASCII paths;
• adds regression tests for filenames containing colons and other special characters;
• verifies the behavior across workspace, commit, and plain-directory search modes.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• go test ./internal/tool
• make check
• make test
• make build

The regression tests cover special-path parsing and binary-result handling, including the result-limit case that previously produced an incorrect matching-file count.

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA
• I used AI/LLM assistance and disclose it below; I reviewed the output, did not attribute the commit to AI, and will answer maintainer questions and review comments myself.

AI Disclosure

I used ChatGPT with GPT-5.6 Sol to assist with debugging and language/writing support. I reviewed the suggested changes and the resulting code myself, and the commit contains no AI attribution trailer.

Related Issues

N/A

[github-actions]

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[CLAassistant]

All committers have signed the CLA.