Source the setup form from the Omarchy runtime (#104)

The keyboard layout list, the account and hostname validation rules, and the
gum prompts that ask for them existed here and again in the runtime's
first-boot owner setup, with nothing keeping the copies honest. They had
already drifted: dropping two layouts from this list moved English (US) from
the top of one gum choose page to the bottom of the previous one, leaving the
preselected default pinned under a screenful of layouts.

The form now lives in the runtime at install/provisioning/setup-form.sh, and
build-iso.sh vendors it out of the very runtime package this ISO bundles —
the same two-branch machinery already used for omarchy-base.packages, so a
--local-source build takes it from the mounted checkout and everything else
extracts it from the downloaded package. An ISO therefore ships the form
belonging to the runtime it installs.

That file is extracted on its own rather than alongside the package lists:
bsdtar exits non-zero for a member it cannot find, so bundling the request
would abort the build under set -e with a bare "Not found in archive" instead
of the actionable error about publishing a runtime that carries the form.

Cancel handling is unified with first-boot setup, which is what made the
prompts shareable. Every prompt reports 0 (answered), 1 (Esc), or 130
(Ctrl+C). Esc now unwinds to the start of the form instead of ending the
install — it previously hit the same `|| abort` as Ctrl+C. Ctrl+C keeps both
of its hidden affordances: arming deferred provisioning on the first keyboard
screen, and toggling unencrypted on the disk screens.

test_keyboard.py reads the layout list from a runtime checkout now, and skips
its localectl coverage rather than failing when there is none to read.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

configs/airootfs/usr/share/omarchy-iso/orchestrator/keyboard.py

@@ -18,8 +18,9 @@ from pathlib import Path
 def configure_keyboard(target: Path, language: str) -> bool:
     """Write the console keymap into a mounted target without booting it.
 
-    Returns False for layouts localectl doesn't know (the configurator offers
-    two, ba and khmer), matching archinstall: warn and keep the default.
+    Returns False for layouts localectl doesn't know, matching archinstall:
+    warn and keep the default. Every layout the configurator offers is known;
+    the guard is for the kb_layout an autoinstall drive can name freely.
     """
     if not language.strip():
         return True