fix: stop Tailwind from scanning runtime data during the build (#465) (#467)

Tailwind v4 detects sources automatically and reads every file under the
project root that is not ignored by git. The app writes repository
backups to data/repo-backups by default, and that directory sits inside
the project root on source installs such as the Proxmox script. With
large git bundles there, the build read them into memory and the
process was OOM-killed at the server entrypoints step.

Limit the Tailwind source scan to src/, which is the only place the app
uses utility classes. This also stops the docs site under www/ from
contributing classes to the app stylesheet. Ignore data/ as a whole in
git, keeping its README.

Verified in an unprivileged LXC with a 2 GiB limit: with a 3 GB file
under data/repo-backups the build was killed, and with this change it
completes. Every class dropped from the stylesheet came from www/,
docs or workflow files, none from src/.

.gitignore

@@ -17,8 +17,9 @@ pnpm-debug.log*
 .env
 .env.production
 
-# database files
-data/gitea-mirror.db
+# runtime data (database, repo backups); keep the README
+data/*
+!data/README.md
 
 # macOS-specific files
 .DS_Store