feat: add rtk wc command for compact word/line/byte counts

[heAdz0r]

Summary

• Adds rtk wc subcommand that compresses wc output (strips padding, shortens paths, returns bare numbers for single-flag modes)
• Single file: 30 96 978 file.py → 30L 96W 978B
• Multi-file: strips common path prefix, replaces "total" with Σ
• Single-flag modes (-l, -w, -c, -m): returns bare number

Changes

File	Change
src/wc_cmd.rs	New module: filter logic, mode detection, common prefix stripping, 15 unit tests
src/main.rs	+12 lines: mod wc_cmd, Wc enum variant, dispatch handler

No hooks, docs, or init template changes — this PR is implementation-only.

Token savings examples

Command	Raw output	RTK output	Savings
wc file.py	30 96 978 scripts/find_duplicate_attrs.py	30L 96W 978B	~75%
wc -l file.py	30 scripts/find_duplicate_attrs.py	30	~90%
wc -l src/*.rs	10+ lines with padded paths	compact table, common prefix stripped	~60%

Test plan

• cargo fmt --all --check passes
• cargo clippy --all-targets clean (no new warnings)
• cargo test wc_cmd — 15/15 tests pass
• Manual test: rtk wc src/main.rs, rtk wc -l src/*.rs

🤖 Generated with Claude Code

[heAdz0r]

CI note: Documentation Validation failure is pre-existing

The Documentation Validation / validate check fails with:

❌ README.md ne mentionne pas version 0.20.1

This is not caused by this PR — the same check fails on master itself:

577e082 (master HEAD) → Documentation Validation: failure
0b34772 (master~1)    → Documentation Validation: failure

The issue is that README.md was not updated after the 0.20.1 release. This PR only adds src/wc_cmd.rs and 12 lines to src/main.rs — no docs touched.

[pszymkowiak]

• cargo fmt --all --check ✅
• cargo clippy --all-targets ✅ (2 minor map_or → is_some_and suggestions, not introduced by this PR)
• cargo test wc_cmd — 15/15 ✅
• Manual test single file: wc src/main.rs → 1437L 4198W 44986B ✅
• Manual test multi-file: wc -l src/*.rs → paths stripped, common prefix removed, Σ 22468 total ✅

Minor nit (non-blocking): Clippy suggests replacing parts.last().map_or(false, ...) with parts.last().is_some_and(...) in two places (lines 205 and 239). Feel free to fix or leave as-is.