fix(grep): accept -n flag for grep/rg compatibility

[heAdz0r]

Summary

• rtk grep -n "pattern" path fails with unexpected argument '-n' because clap rejects unknown flags before positional arguments
• Users naturally place -n before the pattern (muscle memory from grep -n / rg -n)
• The flag is a no-op — grep_cmd::run() already passes -n to ripgrep unconditionally (line 24) — but clap must accept it

Reproduction

rtk grep -n "TODO" src/
# error: unexpected argument '-n' found
#   tip: to pass '-n' as a value, use '-- -n'

Fix

Adds -n/--line-numbers as an explicit bool field to the Grep command enum variant, ignored in the match arm (line_numbers: _). Same pattern as Read command which already defines -n (main.rs:105).

Files Changed

File	Changes	Purpose
src/main.rs	+29	Add -n flag to Grep, ignore in dispatch, add 2 clap parsing tests

Test plan

• cargo fmt --all --check — clean (no formatting changes in main.rs)
• cargo clippy --all-targets — 0 errors
• cargo test — 340 passed
• Manual: cargo run -- grep -n "fn run" src/grep_cmd.rs — works

🤖 Generated with Claude Code

[pszymkowiak]

Thanks for the fix — the approach is clean and correct. Same pattern as the -n flag on the Read command.

The PR has merge conflicts with master (main.rs has changed a lot since Feb 15). Could you rebase on master and force-push? Once the conflicts are resolved, this is good to merge.