feat(setup): show under-the-sea lobster splash at boot

Replaces the single-line `NanoClaw` wordmark printed by
nanoclaw.sh with a multi-line splash frame: the lobster mascot
rendered as truecolor braille, drifting bubbles on either side,
the figlet wordmark below (Nano in bold, Claw in cyan bold),
three taglines — "Small.", "Runs on your machine.", "Yours to
modify." — and a navy seafloor line.

The frame is pre-rendered into `assets/setup-splash.txt` (built
from `assets/nanoclaw-icon.png` via chafa for the lobster +
figlet for the wordmark). nanoclaw.sh just streams the literal
bytes — no runtime dependency on chafa, figlet, or
ImageMagick.

Total height: 30 lines. Visible width: ~40 columns (fits any
terminal). Truecolor ANSI codes are used directly; terminals
without truecolor support will see a degraded but still
readable frame.

Also removes the standalone "Small. Runs on your machine.
Yours to modify." tagline line that nanoclaw.sh used to print
above the bootstrap spinner — those taglines now appear inside
the splash, so showing them again would duplicate.

The wordmark-suppression flow downstream (`setup:auto` honoring
`NANOCLAW_BOOTSTRAPPED=1`) is unchanged: the splash prints once
in nanoclaw.sh, setup:auto's `printIntro()` sees the flag and
keeps the clack `p.intro` line clean ("Let's get you set up.").

assets/setup-splash.txt

@@ -0,0 +1,30 @@
+
+     ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠰⣄⠘⣦⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀   
+     ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢹⡆⢸⡆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀  °
+     ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⡇⢸⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀   
+     ⠀⠀⠀⠀⠀⢀⣠⣴⠾⠟⠛⠛⠿⢶⣦⣾⠇⣾⠁⠀⠀⠀⢀⣤⣤⠀⢀⣄⠀   
+     ⠀⠀⠀⠀⣴⡿⡋⠀⠀⠀⠀⠀⢤⣾⣿⢛⢿⣏⠀⠀⠀⢰⣟⣽⡏⠀⣸⡿⣧   
+   o ⠀⠀⢀⣾⠋⠀⠀⠀⠀⠀⠀⠀⠀⠘⠈⣧⣀⣿⣧⠀⠀⣿⣼⣿⣇⣾⠋⢠⣿   
+     ⠀⠀⣾⢃⠀⢲⣷⡋⣰⡀⢀⣀⣀⡀⠠⣿⣿⣠⣿⣇⠀⣿⢻⣉⠉⠙⠠⣼⠇   
+     ⠀⣼⡏⠃⠀⢸⣿⣿⡿⠃⣾⣷⣻⣿⡏⢹⠿⠿⣿⣿⢀⣿⣐⠙⣷⣦⡾⠋⠀  o
+     ⢠⣿⡃⠀⠀⠀⠀⠀⠈⠀⠀⠉⠙⠁⠀⠀⠀⠐⣿⣿⣟⠁⣿⣿⠟⠋⠀⠀⠀   
+   ° ⢸⣿⣧⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣨⣿⣿⣿⣿⣿⠟⠁⠀⠀⠀⠀⠀   
+     ⢸⣿⣿⣷⣤⣤⠀⣀⢀⠀⢀⣀⣠⣴⣶⣿⣿⣿⣿⡿⠛⠁⠀⠀⠀⠀⠀⠀⠀   
+     ⣿⢋⠿⣿⣿⣿⣿⡿⣿⣿⣿⣿⣿⣿⠿⠿⠿⣿⣅⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀  O
+     ⣿⣿⠙⢾⣽⣟⣿⣿⣼⣿⣿⣿⣩⣶⣶⣦⠀⠀⠩⢻⣆⠀⠀⠀⠀⠀⠀⠀⠀   
+     ⠘⣿⣶⣤⣿⣿⣿⣿⣵⢖⡀⠉⠹⡛⢷⣝⡿⠁⠀⠀⣿⡆⠀⠀⠀⠀⠀⠀⠀   
+     ⠀⢹⣯⣽⣟⣛⣻⣿⣿⣾⣽⢶⣽⣿⣿⣿⣏⠀⠠⣤⣿⡇⠀⠀⠀⠀⠀⠀⠀   
+     ⠀⠀⠻⣿⣶⣾⣿⢿⣻⣿⣿⣿⣿⣿⣿⣏⣛⣧⣦⣿⣿⣧⣄⠀⠀⠀⠀⠀⠀   
+   o ⠀⠀⠀⠈⠻⣿⣶⣥⣼⣿⣿⣽⣿⣿⣿⣷⣶⣾⣿⣿⣯⣘⣿⣧⠀⠀⠀⠀⠀   
+     ⠀⠀⠀⠀⠤⣤⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠿⠿⠿⠋⠀⠀⠀⠀⠀   
+
+ _  _                 ___ _             
+| \| |__ _ _ _  ___  / __| |__ ___ __ __
+| .` / _` | ' \/ _ \| (__| / _` \ V  V /
+|_|\_\__,_|_||_\___/ \___|_\__,_|\_/\_/ 
+
+                 Small.
+         Runs on your machine.
+            Yours to modify.
+
+════════════════════════════════════════