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

apps/frontend/.env.example

@@ -1,3 +0,0 @@
-BASE_URL=https://api.modrinth.com/v2/
-BROWSER_BASE_URL=https://api.modrinth.com/v2/
-PYRO_BASE_URL=https://archon.modrinth.com/

apps/frontend/.env.local

@@ -0,0 +1,5 @@
+BASE_URL=http://127.0.0.1:8000/v2/
+BROWSER_BASE_URL=http://127.0.0.1:8000/v2/
+PYRO_BASE_URL=https://staging-archon.modrinth.com
+PROD_OVERRIDE=true
+