fix(grep): adjust the command to fall through if the output would already be as small as possible

[JBF1991]

Summary

Fix rtk grep compatibility with standard grep format flags (-c, -l, -L, -o, -Z). These flags change output shape so fundamentally that RTK's grouped formatter produced garbage or ignored the flag entirely.

Root Cause

• Issue: bug(grep): -c count flag ignored — returns match summary + context instead of line count #1452
• rtk grep hardcoded -n --no-heading into rg regardless of user flags.
• The output parser assumed file:line:content format, so -c output (file:count) was misinterpreted.
• Clap's context_only: bool had #[arg(short, long)], which captured -c before it reached extra_args.

Test plan

All tests pass:

$ rtk cargo test --all
cargo test: 1680 passed, 6 ignored

Format flags now produce raw output:

Flag	Command	Output
-c	rtk grep -c "fn run" src/cmds/system/grep_cmd.rs	1
-l	rtk grep -l "fn run" src/cmds/system/grep_cmd.rs	src/cmds/system/grep_cmd.rs
-L	rtk grep -L "nonexistent" src/cmds/system/grep_cmd.rs	src/cmds/system/grep_cmd.rs
-o	rtk grep -o "fn" src/cmds/system/grep_cmd.rs	fn\nfn\nfn...

Normal path unchanged:

$ rtk grep "fn run" src/cmds/system/grep_cmd.rs
1 matches in 1F:

[file] src/cmds/system/grep_cmd.rs (1):
    12: pub fn run(

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

[aeppling]

Blockers

1. Missing --no-ignore-vcs in passthrough path

The duplicated rg command construction forgot --no-ignore-vcs (added by #791 to fix false negatives on gitignored files).

Result: rtk grep "pattern" . searches gitignored files, rtk grep -c "pattern" . does not. Same pattern, different results depending on output flag.

2. -l / --files-with-matches is dead code

Clap captures -l as max_len (#[arg(short = 'l', ...)]) before it reaches extra_args. Users get a parse error, not file listing. Same class of bug this PR fixed for -c.

Root cause: both bugs come from duplicating the command construction

The passthrough path copies ~25 lines of rg command setup instead of reusing it. Fix both bugs at once by moving the has_format_flag check to after execution, before formatting:

// existing rg command construction (unchanged, includes --no-ignore-vcs)
let result = exec_capture(&mut rg_cmd).or_else(|_| { /* grep fallback */ })?;

if has_format_flag(extra_args) {
    print!("{}", result.stdout);
    if !result.stderr.is_empty() {
        eprintln!("{}", result.stderr.trim());
    }
    timer.track_passthrough(...);
    return Ok(result.exit_code);
}

// existing formatter (unchanged)

No duplication, no flag drift, --no-ignore-vcs inherited automatically.

[JBF1991]

I wasn't aware of #791 when I pushed this up. Sorry! I will update it accordingly.

[JBF1991]

@aeppling I went ahead and made the change with slight tweaks to avoid empty spaces in the db when there was a pass-through.

[aeppling]

LGTM, thanks for contributing @JBF1991

Will be released during the week