Fix first-run login loop caused by unpackaged user units

[megabyte0x]

Fixes #366.

Problem

omarchy-brightness-keyboard-auto.service and omarchy-speaker-tuning.service ship as source under /usr/share/omarchy but never land in /usr/lib/systemd/user/, because the omarchy-settings PKGBUILD installs user units from a hand-maintained list. install/user/first-run/enable-user-units.sh enabled every unit in a single systemctl --user enable --now call under set -euo pipefail, so the one missing unit failed the whole step, first-run-user was never marked done, and the entire first-run notification stack replayed at every login.

Changes

• build-packages.sh: new install_all_user_units() patches the omarchy-settings PKGBUILD at build time (same non-forking rewrite mechanism as strip_limine_dependencies / keep_apple_silicon_mkinitcpio_drop_ins) with a glob loop that installs every default/systemd/user/*.service. It fails loudly if upstream restructures the install anchor.
• install/user/first-run/enable-user-units.sh: enables units one at a time, warns per failing unit, and no longer fails the first-run step. A failed daemon-reload still fails, so a dead user manager retries next login.
• migrations/1788782695.sh: repairs wedged machines — removes the dangling graphical-session.target.wants symlink migration 1788139121 left behind and re-runs the enable. Idempotent; stays pending without a live user manager.
• Tests: enable-user-units-test.sh, first-run-units-migration-test.sh, user-units-packaging-test.sh (regression: every referenced omarchy user unit must ship, and the build must glob-install them), plus new assertions in install-mac-test.sh and a pinned migration lookup in brightness-keyboard-auto-test.sh.

Verification

• ./test/all — only pre-existing failures remain (config-test.sh / unowned-system-paths-test.sh need an omarchy-pkgs checkout; runtime-smoke-test.sh fails identically on quattro at 291a698)
• bin/omarchy commands --check — passed (458 commands)
• bash -n / ast.parse over bin/omarchy-* — clean
• Negative check: hiding default/systemd/user/omarchy-brightness-keyboard-auto.service makes user-units-packaging-test.sh fail, proving it would have caught the 4.0.2 bug

Plan: plans/first-run-loop-missing-units-fix.md

[malik-na]

Please do not swallow enable failures for every user unit. A transient failure of sleep-lock or migrate-notify would mark first-run complete and never retry. Tolerate only the known missing-unit case, and limit migration cleanup to the known dangling link instead of deleting every dangling service symlink.