refactor: remove better-auth login and registration pages

- Deleted the login page and its associated server logic for better-auth.
- Removed the Playwright demo page and its test file.
- Updated layout CSS to include new theme variables and font imports.
- Added Geist Mono and Inter font files along with their licenses.
- Configured D1 database in wrangler.jsonc for Cloudflare Workers.

Author: NotReeceHarris

drizzle/0001_slow_gambit.sql

@@ -0,0 +1,3 @@
+ALTER TABLE `user` ADD `username` text;--> statement-breakpoint
+ALTER TABLE `user` ADD `display_username` text;--> statement-breakpoint
+CREATE UNIQUE INDEX `user_username_unique` ON `user` (`username`);