Homepage (TDD slice 6): the git-driven deploy

Red tests first.
- tests/homepage_deploy.bats: the deploy ships the homepage (assets to
  /srv/homepage, the checker timer, both Caddy hashes, deployed.js) and is
  git-driven (pulls main); the checker runs as a systemd timer.
- scripts/homepage-status.service / .timer: the checker as a oneshot service
  + a 3-minute timer (Q2/Q35).
- scripts/deploy.sh: the Caddyfile render now substitutes BOTH hashes
  (REPLACE_WITH_HASH <- CADDY_BASICAUTH_HASH, REPLACE_WITH_ADMIN_HASH <-
  CADDY_ADMIN_HASH). A new homepage step copies the assets to /srv/homepage,
  generates deployed.js from the deployed commit's datetime (Q43), installs
  the checker timer, and runs the checker once so status.json exists at once.
- tests/llm_units.bats: scoped the three LLM-unit tests to
  frank-default-*.service (the homepage unit is a different pattern: it
  installs to /usr/local/bin and runs from /srv at deploy time).

scripts/homepage-status.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=Run the homepage status checker every 3 minutes
+
+[Timer]
+OnBootSec=1min
+OnUnitActiveSec=3min
+Unit=homepage-status.service
+
+[Install]
+WantedBy=timers.target