fix(setup): point setup-keyboard at the provisioning form

[duketopceo]

Summary

Fixes #408.

omarchy setup keyboard still looked for install/first-run/keyboard-layout.sh, which 75cb4f7 ("Make setup ISO-only") removed, so the command exited with a missing-script error and no picker ever appeared.

The rewrite sources install/provisioning/setup-form.sh — the same layout table and gum picker first-boot provisioning uses, so the command can never offer a layout setup could not apply — then persists the choice through localectl:

• localectl set-keymap writes KEYMAP= for the console
• localectl --no-convert set-x11-keymap writes XKBLAYOUT/XKBVARIANT to /etc/vconsole.conf and the xorg drop-in
• default/hypr/input.lua already reads XKBLAYOUT from vconsole.conf, so a hyprctl reload applies the layout to the running session — no relaunch needed
• Esc and Ctrl+C leave the current layout untouched

Both calls go through polkit, so the active session user needs no sudo (verified on a 4.0.3-1 package install). Also drops the hardcoded $HOME/.local/share/omarchy path for $OMARCHY_PATH with the standard /usr/share/omarchy fallback — the old default made the error message point at a path that only exists on dev checkouts.

Test plan

• New tests/test-setup-keyboard.sh stubs gum/localectl/hyprctl: UK pick persists uk+gb, Dvorak passes the variant through, cancel writes nothing (6/6 pass)
• ./test/all green (3 unrelated env failures — no omarchy-pkgs checkout here)
• bin/omarchy commands --check passes (465 commands)
• Real run on M1 Pro 4.0.3-1: current layout shown, picker renders (previously instant crash)
• Interactive pick on a live session (gum UI verified rendering; apply path covered by stub test)

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