Sync Omarchy theme to Opencode

[p134c0d3]

Generates an Opencode file theme from colors.toml on every theme switch and syncs it to ~/.config/opencode/themes/omarchy.json, so Opencode follows the Omarchy theme. Open sessions retint live via SIGUSR2 without a restart. Opt in once with omarchy-theme-set-opencode --activate (mirrors the claude/pi sync scripts).

Reloads target interactive TUIs only: the background service (opencode serve --service) does not handle SIGUSR2, so the previous killall -SIGUSR2 opencode killed the service on every theme switch instead of refreshing. Both the new sync script and omarchy-restart-opencode now skip service processes.

Notes:

• The template uses the file theme format (same shape as the built-in themes and .opencode/themes/mytheme.json upstream). The newer version-2 documented format with partial keys did not apply on 0.0.0-beta-19500 in testing (theme silently falls back to built-in), so this ships the complete key set that was verified to load and live-refresh.
• Verified end to end on beta-19500: template renders with zero placeholders left (including palettes missing derived keys like orange), sync + activation preserve unrelated cli.json settings, and a running TUI switched Mandalorian -> Tokyo Night -> Mandalorian purely via file sync + SIGUSR2 (confirmed by reading the TUI's emitted truecolor sequences).
• Tests: new theme template/sync/activation coverage in ./test/cli (10 assertions) plus test/shell.d/opencode-refresh-test.sh for the TUI-only signaling of both scripts. Full ./test/cli passes (126 ok); ./test/shell shows only the pre-existing environmental failures (missing omarchy-pkgs checkout, non-executable snapper test).

Screenshots of the running TUI under each theme to follow (attached via web UI).