feat(gcc): add gcc/g++/clang compiler output filter

[cardillo]

Adds rtk gcc command that groups diagnostics by file, strips verbose caret/source-snippet context lines, and shows a compact BUILD FAILED summary or warnings-only view.

• 60-80% token savings on typical compiler output
• Handles gcc, g++, clang, clang++ (via --compiler flag)
• Strips "In file included from", caret (^), pipe (|) context lines
• Groups errors by file, sorted by error count descending
• Preserves make error lines for CI/CD exit-code context
• 13 unit tests covering all paths, including token savings assertions
• Registered in discover/rules.rs for automatic hook rewriting

https://claude.ai/code/session_01WfWYojKvkiHdDDHQbYcAyz

Summary

• Output filter for c/c++ compile commands from gcc and clang

Test plan

Running locally and automated test suite.

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

✨ Type	feature
🟢 Risk	low

Summary

Adds a new rtk gcc output filter command that parses and compacts gcc/g++/clang/clang++ compiler diagnostics. It groups errors and warnings by file, strips verbose caret/source-snippet context lines, and provides a compact BUILD FAILED or warnings-only summary with 60-80% token savings. Includes 13 unit tests and registration in the discovery/rules system.

Review Checklist

• Tests present
• Breaking change
• Docs updated

---

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

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}