feat: add xcodebuild support

[rursache]

Summary

• add a dedicated rtk xcodebuild command with mode-aware output handling for build-like, test, info, and fallback invocations
• preserve high-value xcodebuild test context while stripping repetitive build noise, and keep -list / -showBuildSettings near-lossless
• wire xcodebuild into CLI discovery, auto-rewrite hooks, docs, smoke coverage, and hook rewrite tests

Details

• added [x] src/xcodebuild_cmd.rs with conservative filtering, raw fallback behavior, -v passthrough, and exit-code propagation
• added fixture-driven and fake-binary test coverage for build success/failure, test success/failure, archive/export, and info output
• registered xcodebuild in src/main.rs, src/discover/rules.rs, and src/discover/registry.rs
• updated .claude/hooks/rtk-suggest.sh and hooks/test-rtk-rewrite.sh
• updated README / INSTALL / ARCHITECTURE / CLAUDE docs and validation scripts

Verification

• cargo test --quiet
• bash hooks/test-rtk-rewrite.sh
• bash scripts/validate-docs.sh
• cargo run --quiet -- xcodebuild --help

Closes #376

[aeppling]

This should be merged in develop branch following https://github.com/rtk-ai/rtk/blob/master/CONTRIBUTING.md and #380 announcement

[rursache]

Closing this in favor of #394, which follows the new contribution flow from discussion #380 and targets develop.