#26 Owner block-art logo (ansi + plain)

Context: Owner supplied the official hu13 block-art logo (12-line ANSI terminal art, magenta/cyan/grey on Tokyo Night). It replaces the provisional line-art banner. Raw ANSI original: 12 lines (kept verbatim in this issue body? NO — stored as static/logo-ansi.txt). Plain render (ANSI stripped): block glyphs reading "hu13". Tasks:

1. static/logo-ansi.txt: owner's 12 lines VERBATIM including all [...m codes (supervisor has the exact text in /tmp/hu13plan/owner-art-raw.txt — copy byte-for-byte, do not retype).
2. static/ascii.txt: plain version (ANSI stripped, sed 's/\[[0-9;]*m//g'). Must read "hu13" in block glyphs, 12 lines. Used by wiki README + logo::ascii_pre (web <pre>).
3. Purity test update (tests/logo.rs): ascii.txt charset becomes block set (space + █ ▓ ▒ ░ ▄ ▀ ▌ ▐ + existing | - / _) — still no letters, no <>&. New test: stripping ANSI from logo-ansi.txt yields ascii.txt byte-for-byte. ANSI file itself: assert it contains ESC-free [...m codes + block glyphs (it is stored with literal codes, not raw ESC bytes — see raw file).
4. Terminal use: print logo-ansi.txt (interpreted — terminal renders colors) in hu13 --version? Decide: YES, small — append plain banner after version ONLY when stdout is a tty (no ANSI dump into pipes). Keep zero-dep (own isatty via std? std::io::IsTerminal — stable, use it).
5. wiki README: already shows old banner — rebuild picks up new art automatically (verify in dogfood). Success rubric:

• --version on tty shows colored banner; piped shows plain version line only.
• ascii.txt renders "hu13" in <pre>; strip-test green; purity test green.
• No raw ESC bytes in repo (grep -r $'\x1b' static/ | empty). Swarm: Owl. Branch m6/owner-logo. STATUS: FILED — WAIT FOR OWNER GO-AHEAD before dispatch (owner said "then wait").