Confine Quattro overwrite to ownership bootstrap

[ryanrhughes]

Release gate: do not merge yet

This 3.x stable bootstrap must not merge until the fixes in #9070 and omacom/omarchy-pkgs#239 have shipped together as v4.0.2. Merging it earlier could send a 3.x user through the ownership transition with the older 4.0.1 package payload.

What changed

• The 3.x to Quattro upgrader uses --overwrite='*' exactly once, only while installing omarchy-settings to adopt the known legacy configuration paths.
• The core package install, audio transition, and final package sync use normal Pacman semantics with no overwrite.
• Stable, rc, and edge upgrades select their matching package repositories; rc uses the production release-candidate pair and dev packages are edge-only.
• A focused regression test prevents wildcard overwrite from spreading back into steady-state installs.

This is only the legacy launcher side of the transition. #9070 supplies the Quattro-side fail-closed updater and exact legacy cleanup, while omacom/omarchy-pkgs#239 supplies the package-owned static system state.

Proof

bash test/upgrade-to-quattro-ownership-test.sh

Rollout

After v4.0.2 is published, merge this PR. Existing 3.x stable users should run omarchy update before selecting the Quattro upgrade so their branch-local launcher contains this constrained ownership bridge. The official https://omarchy.org/upgrade-to-quattro endpoint already fetches the Quattro implementation directly.

Companion 3.x channel PRs: rc #9073 and dev #9071.