fix(grep): translate BRE \| alternation and strip -r flag for rg

[heAdz0r]

Summary

• rtk grep "fn foo\|fn bar" src/ returns 0 results silently — users coming from grep/awk muscle memory use BRE \| for alternation, but rg uses PCRE-style |; rg receives the literal \| and finds nothing.
• rtk grep "pattern" src/ -r returns 0 results silently — in rg, -r means --replace (requires an argument); passing it alone causes rg to exit with an error. The .or_else(|_| ...) IO-fallback never triggers on a non-zero exit, so stdout is empty.

Reproduction

# Bug 1: BRE alternation
rtk grep "fn run\|fn new" src/
# 🔍 0 for 'fn run\|fn new'   ← should find many matches

# Bug 2: -r flag
rtk grep "pattern" src/ -r
# 🔍 0 for 'pattern'          ← should find matches (rg is recursive by default)

Fix

Bug	Root cause	Fix
| alternation	rg doesn't understand BRE alternation	pattern.replace(r"|", "|") before passing to rg (grep_cmd.rs:23)
-r flag	rg -r = --replace (needs arg), not recursive	Filter out -r/--recursive from extra_args; rg is recursive by default (grep_cmd.rs:33-36)

Files Changed

File	Changes	Purpose
src/grep_cmd.rs	+28 / -1	Both fixes + 2 regression tests

Test plan

• cargo fmt --all --check — clean
• cargo clippy --all-targets — 0 errors (pre-existing warnings only)
• cargo test grep_cmd:: — 8 passed
• Manual: rtk grep "fn run\|fn new" src/grep_cmd.rs — finds matches
• Manual: rtk grep "pattern" src/ -r — no longer breaks

🤖 Generated with Claude Code

[pszymkowiak]

Thank you! Good catch on both issues — silent 0 results is a real pain for users coming from grep.