feat(eza): add token-optimized eza filter

[Sathvik-1007]

Closes #1030

What

rtk eza — filter proxy for eza (modern ls replacement). 3 modes, noise stripped, tokens saved.

Modes

Mode	What gets stripped	Savings
flat (default)	noise dirs, icons, cap 30 entries	~3-65%
long (-l)	perms, user, timestamps → name + size only	~70%
tree (-T)	noise dir subtrees via --ignore-glob, summary line	~89-94%

Flag-aware

• -a/--all/--almost-all → skip noise filtering, show everything
• --git column → detected, parsed correctly (not confused with size)
• --oneline/-1 → flat mode, minimal already, still caps at 30
• --icons → stripped from output (nerd font chars removed)
• --ignore-glob already set → we don't override user's glob
• --level=N → passed through, no interference

Implementation

• src/cmds/system/eza_cmd.rs — 414 lines, 21 unit tests
• run() → runner::run_filtered() + RunOptions::stdout_only().early_exit_on_failure()
• filter_flat(), filter_long(), filter_tree() — pure &str → String
• strip_icon() — finds first ASCII byte, trims nerd font prefix
• is_size_like() — distinguishes git status cols (M-, N-) from sizes (4.0k, -)
• parse_long_line() — field-split parser, no regex needed
• Reuses NOISE_DIRS from constants.rs
• RtkRule added in rules.rs (pattern ^eza(\s|$), savings 70%)

Tests

• 21 unit tests covering all modes, edge cases, icon stripping, git columns
• cargo fmt + clippy + test → 1371 passed, 0 failed, 6 ignored
• E2E verified: flat, long, tree, -a, -1, error path, --git

Docs updated

• CHANGELOG.md
• README.md (command list + mapping table)
• src/cmds/system/README.md

Not tested

• Windows (Linux only)
• macOS (should work — same eza output format)

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