Make Brave Origin the default browser for new installs

[tsmartt]

Omarchy deserves a browser with world-class adblocking built in, so I'm proposing this PR.

Fresh installs currently ship and select Chromium. Make Brave Origin the default browser, with Omarchy's theme, Wayland flags, and bundled extensions configured during installation.

• Replace Chromium in the base package manifest and select Brave Origin for new-user browser and HTTP/HTTPS defaults.
• Use Brave Origin for web apps when the selected browser does not support app windows, and when an optional default browser is removed. Preserve Chromium fallbacks on existing installations, including newly created users, and refuse removal when no replacement default can be selected.
• Offer Chromium in the optional browser menus, recognize Brave Origin's window class, and install the 1Password browser extension for Brave Origin. Update the manual and fresh-install acceptance expectations.

Existing users retain their selected browser and profile data.

Related: #6534

Depends on publishing brave-origin-bin from omacom/omarchy-pkgs#326 before an ISO is built with this manifest. omacom/omarchy-iso#159 updates clipboard acceptance to launch the default browser.

Validation: 13 focused shell suites and test/cli pass in an x86_64 Arch Linux container. The real omarchy and omarchy-settings package functions successfully assemble the new manifest, seeded flags, MIME defaults, and extension files. Bash syntax checks and ShellCheck at error severity pass. Brave Origin 1:1.94.121-1 builds from the checksum-verified AUR sources, installs, and reports its version.

A fresh x86_64 ISO built from the three companion commits installs successfully. On its first desktop session, xdg-settings and the HTTP, HTTPS, and HTML MIME handlers all select brave-origin.desktop; Chromium is absent; Omarchy's flags, policies, and three bundled extensions are present; and the default-browser launcher starts Brave Origin and maps its window.

The broader bin-style-test.sh fails on existing command -v calls in omarchy-remove-ai-openclaw and omarchy-remove-ai-hermes; the same failure reproduces on the unchanged base. The aarch64 browser build was not run.