Add cross-seam regression tests that prove theme orchestration earns its depth

[mswell]

Parent

#30

What to build

Add cross-seam regression tests that prove theme orchestration earns its depth. The tests should exercise behavior through the public theme orchestration interface and stable dry-run/fake-apply surfaces, not by depending on the private shape of the action catalog.

This final slice should demonstrate that deleting theme orchestration would re-spread desktop rules across scripts and that future refactors keep dry-run planning and host apply behavior aligned.

Acceptance criteria

• Tests verify dry-run output includes expected persistence, symlink, write, set, check, and reload actions.
• Tests verify fake apply behavior crosses the theme orchestration seam without mutating the real desktop.
• Tests prove unsupported themes fail with usage text.
• Tests prove portal mismatch warnings still happen.
• Tests prove browser profile edits remain absent.
• Test names and assertions use the dotfiles domain vocabulary for theme orchestration.

Blocked by

• Route theme symlink orchestration through the shared action catalog #46
• Represent generated desktop settings as catalog write/set/check actions #47
• Put reload and optional desktop-tool behavior behind a safe adapter #49
• Catalog component-specific theme mutations without browser profile edits #50
• Harden theme resolution, usage guidance, and supported-theme locality #52