feat: Overhaul client-side navigation and clean up project

- Implement a unified SPA routing system in nav.js, removing all legacy and conflicting navigation scripts (router.js, inject-nav.js, fix-nav.js).
- Refactor dashboard.js to delegate all navigation handling to the new nav.js module.
- Create new modular JS files (auth.js, personal-player.js, logger.js) to improve code organization.
- Fix all navigation-related bugs, including guest access and broken footer links.
- Clean up the project root by moving development scripts and backups to a dedicated /dev directory.
- Add a .gitignore file to exclude the database, logs, and other transient files from the repository.

static/streams-ui.js

@@ -1,5 +1,5 @@
 // static/streams-ui.js — public streams loader and profile-link handling
-import { showOnly } from './router.js';
+
 import { globalAudioManager } from './global-audio-manager.js';
 
 // Global variable to track if we should force refresh the stream list