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/magic-login.js

@@ -1,5 +1,5 @@
 // static/magic-login.js — handles magic‑link token UI
-import { showOnly } from './router.js';
+import { showSection } from './nav.js';
 
 let magicLoginSubmitted = false;
 
@@ -73,8 +73,8 @@ export async function initMagicLogin() {
           if (registerPage) registerPage.style.display = 'none';
           
           // Show the user's stream page
-          if (window.showOnly) {
-            window.showOnly('me-page');
+          if (typeof showSection === 'function') {
+            showSection('me-page');
           }
         });
         return;