etherpad: switch default DB to sqlite + use canonical ether/etherpad repo refs

- ct/etherpad.sh + install/etherpad-install.sh: use ether/etherpad
  (canonical name; ether/etherpad-lite still redirects but the new
  name is preferred)
- install/etherpad-install.sh: switch dbType from dev-only "dirty"
  to sqlite at /var/lib/etherpad/etherpad.db on first config seed;
  matches the same default we land on across the snap, .deb, and
  Home Assistant add-on packagings
- json/etherpad.json: refresh note to reflect the sqlite default
  and document postgres/mysql as alternatives via dbType/dbSettings

json/etherpad.json

@@ -33,7 +33,7 @@
   },
   "notes": [
     {
-      "text": "The default install uses the built-in DirtyDB store, intended for evaluation only. For production, edit /opt/etherpad-lite/settings.json and switch the 'dbType' to mysql or postgres.",
+      "text": "The default install uses an embedded sqlite database at /var/lib/etherpad/etherpad.db — ACID, zero-config, suitable for single-instance homelab use. To use postgres or mysql instead, edit /opt/etherpad-lite/settings.json and switch 'dbType' + 'dbSettings' (Etherpad's ueberdb abstraction supports both).",
       "type": "info"
     },
     {