fix(gh): rewrite gh search commands

[season179]

Summary

• Rewrite gh search ... commands through rtk gh so hook-based integrations no longer leave GitHub search output raw.
• Require a real gh subcommand boundary so lookalikes like gh searching or gh repository do not get rewritten.
• Add regression coverage for gh search repos/issues/prs/code/commits, structured-output passthrough flags, and false-positive subcommand prefixes.

Fixes #1484

Test plan

• rtk cargo +1.92.0 test test_rewrite_gh_search -- --nocapture
• rtk cargo +1.92.0 test test_rewrite_gh_search_structured_output_skipped -- --nocapture
• rtk cargo +1.92.0 test test_rewrite_gh_subcommands_require_word_boundary -- --nocapture
• rtk cargo +1.92.0 test test_classify_gh_search -- --nocapture
• rtk cargo +1.92.0 test test_all_patterns_are_valid_regex -- --nocapture
• rtk cargo +1.92.0 fmt --all -- --check
• rtk cargo +1.92.0 clippy --all-targets (passes with existing warnings)
• rtk git diff --check
• Manual: rtk cargo +1.92.0 run --quiet -- rewrite 'gh search repos foo --limit 5' rewrites to rtk gh search repos foo --limit 5
• Manual: gh search structured output flags (--json) do not rewrite
• Manual: false positives like gh searching foo do not rewrite

[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟢 Risk	low

Summary

Adds support for rewriting gh search subcommands (repos, issues, prs, code, commits) through rtk gh by extending the existing regex pattern. Introduces a word boundary check ((?:\s|$)) to prevent false positives on similar-looking subcommands like gh searching. Structured output flags (--json, --template) are correctly skipped from rewriting.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #1484

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Analyzed automatically by wshm · This is an automated analysis, not a human review.