fix(ls): fall back to raw output when ls binary is eza/exa/lsd (#1321)

[pszymkowiak]

Summary

• rtk ls returned (empty) for non-empty directories when the ls binary on PATH was eza, exa, or lsd
• Root cause: eza uses day-first dates (22 Apr 14:30) vs POSIX month-first (Apr 22 14:30) — the regex anchor never matched, every line was silently dropped
• Fix: track any_content_line + parse_hit in compact_ls; return a sentinel when output was present but nothing parsed, triggering a raw passthrough with a warning

Behaviour change

Scenario	Before	After
eza as ls on PATH	(empty) ❌	eza raw output + warning ✅
Standard /bin/ls	filtered output ✅	unchanged ✅
Truly empty directory	(empty) ✅	unchanged ✅

No token savings on eza output (passthrough). A follow-up PR could add an eza-aware parser.

Test plan

• 19 existing ls unit tests pass (cargo +nightly test cmds::system::ls)
• New regression test test_compact_eza_format_returns_sentinel added
• Manually tested with PATH=/tmp/eza-test-path:$PATH rtk ls src/ (eza symlinked as ls)
• Truly empty directory still returns (empty)
• cargo +nightly fmt and cargo +nightly clippy clean

Fixes #1321

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[ashokgelal]

I can reproduce this as well.

In my shell, ls is provided by lsd (ls='lsd -l'), and rtk ls returns (empty) in non-empty directories for some flag combinations.

Examples that fail for me:

• rtk ls -1A .
• rtk ls -1 .
• rtk ls -ltT .

Examples that work:

• rtk ls -A .
• rtk ls -lt .

This looks consistent with the bug fixed in this PR.

[ashokgelal]

Additional data point from my side:

Even after removing lsd from PATH and confirming ls resolves to /bin/ls, I still see this:

which ls
# /bin/ls

rtk ls -1A
# (empty)

rtk /bin/ls -1A
# <lists files correctly>