fix(grep): support piped stdin input

[CtriXin]

Summary

rtk grep <pattern> now reads from stdin when input is piped (e.g. ps aux | rtk grep bash), matching plain grep behavior.

Root cause: rtk grep always invoked rg/grep on the filesystem path, ignoring stdin even when the shell had piped data available.

Fix: detect non-tty stdin via std::io::IsTerminal, read and filter lines directly, and output matching results in the same grouped format.

Also handles:

• grep -c via stdin (returns bare integer)
• -i case-insensitive flag via stdin

Fixes: #1476

Test Plan

• cargo test grep_cmd — 9 tests pass
• Manual: ps aux | rtk grep bash returns matching lines
• Manual: echo -e "foo\nbar\nfoo" | rtk grep foo returns 2 matches

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[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟡 Risk	medium

Summary

Adds stdin pipe support to rtk grep so it can filter piped input (e.g. ps aux | rtk grep bash), matching standard grep behavior. The fix detects non-tty stdin via IsTerminal, reads lines directly, and outputs matches in the existing grouped format, with support for -c (count) and -i (case-insensitive) flags.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #1476

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

[gene1wood]

This PR seeks to achieve what #881 was trying to achieve before it was closed. This should address #838 and my duplicate #1476

[KuSh]

Thanks for this. Piped stdin for rtk grep landed on develop in #3128 (merged 23 July 2026), which moved grep into src/cmds/system/search.rs and streams piped input instead of searching the filesystem; the -c and -i cases you added are covered there too, and the grep_cmd.rs module this PR edits no longer exists. Verified against a current develop build: piping into rtk grep returns the matching lines, rtk grep -c returns the count, and rtk grep -i matches case-insensitively. Closing as covered, but if some part of your case is still broken please comment here or reopen.

[gene1wood]

It looks like the underlying stdin-reading fix landed in #2641 (commit 37ee6cf, "fix(grep): match real grep output and read piped stdin"), which reads piped stdin instead of injecting . into the search. Just leaving this hear as a breadcrumb for the future.