Some small Labrinth refactors and fixes (#3698)

* chore(labrinth): fix typos, simplify out `remove_duplicates` func

* fix(labrinth): implement `capitalize_first` so that it can't panic on wide chars

* chore(labrinth): refactor out unneeded clone highlighted by nightly Clippy lints

* chore(labrinth): simplify `capitalize_first` implementation

* fix(labrinth): preserve ordering when deduplicating project field values

This addresses an unintended behavior change on
157647faf2.

* fix(labrinth/tests): make `index_swaps` test run successfully

I wonder why we don't run these more often...

* refactor: rename `.env.example` files to `.env.local`, make local envs more consistent between frontend and backend

* chore(labrinth/.env.local): proper email verif. and password reset paths

packages/app-lib/.env.local

@@ -0,0 +1,2 @@
+# SQLite database file location
+DATABASE_URL=sqlite:///tmp/Modrinth/code/packages/app-lib/.sqlx/generated/state.db