fix: preserve native output in pipelines

[lindicaphxag-tech]

Summary

• Preserve native stdout for every pipeline producer so downstream commands receive the output format they expect.
• Keep safe rewriting of final grep and rg stages.
• Remove the producer-stage safety metadata and update the discover documentation and hook regression coverage.

Fixes #4364.

Validation

• cargo +stable fmt --all -- --check
• cargo +stable test discover::registry::tests:: (456 passed)
• cargo +stable test test_claude_pipeline_preserves_producer_output_for_consumer (passed)
• Full cargo +stable test: 3772 passed, 8 ignored, 13 failed because this Windows environment cannot spawn the Unix shell commands required by existing core::shell / core::stream tests.

[rtk-wshm-sync-bot]

wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟡 Risk	medium

Summary

This PR changes the pipeline rewrite engine so that producer and intermediate stages of a shell pipeline are always left raw (native stdout), only rewriting a final grep/rg stage when safe. It removes the previously added producer-stage rewriting logic and its associated safety-check helpers, and updates the discover README and regression tests accordingly.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #4364

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

[lindicaphxag-tech]

Validation on current head 5c0d5ea: cargo fmt --all -- --check passes; the changed areas pass cargo test --bin rtk discover:: --quiet (627 tests) and cargo test --bin rtk hooks::hook_cmd --quiet (142 tests). A full Windows run passed 3,784 tests with one unrelated ind exit-code assertion differing because C:\Windows\System32\find.exe is selected instead of POSIX find; the changed suites are green. Could a maintainer review whether leaving pipeline producer/intermediate output native is the right boundary for #4364? I can adjust if needed.