review fixes: light-mode contrast, tz robustness, deploy copy

- admin: maroon buttons use .danger class (white text); replace hardcoded
  #333/#ff8a8a/drop-target colors with theme vars so light mode is legible
- time.ts: force hourCycle h23 (no 24:00 artifact), drop dead 24-guard
- Makefile/README: rsync with excludes instead of `cp -a .` so .git and the
  dev DB don't ship to /opt; add rsync to deps

README.md

@@ -105,7 +105,7 @@ sudo useradd --system --no-create-home --shell /usr/sbin/nologin wutzcalc
 
 # 2. Install the built app (run `pnpm install && pnpm build` first)
 sudo mkdir -p /opt/wutzcalc
-sudo cp -a . /opt/wutzcalc            # or rsync/checkout into place
+sudo rsync -a --exclude='.git' --exclude='*.db*' ./ /opt/wutzcalc/
 sudo chown -R root:root /opt/wutzcalc # app dir stays read-only to the service
 
 # 3. Config + secrets (chmod 600 — holds ADMIN_PASSWORD)