Replace Psalm with PHPStan + PHP‑CS‑Fixer + Biome, add linting configs & cleanup

- Removed the `vimeo/psalm` dependency and all related files
(`psalm.xml`, `psalm‑baseline.xml`, suppress annotations).  
- Added **PHPStan** (v2.1.54) and **PHP‑CS‑Fixer** (v3.95.1) to
`vendor/bin/`.  
- Created `phpstan.neon` (level 5, bootstraps `app/bootstrap.php`,
scans `Parsedown.php`).  
- Created `phpstan‑baseline.neon` with 10 pre‑existing errors.  
- Added `.php‑cs‑fixer.dist.php` (PSR‑12 + PHP80Migration, targets
 `app/src` & `app/tests`).  
- Added `biome.json` and updated `justfile` to replace the old Psalm
recipes with `phpstan`, `cs‑check`, and `cs‑fix`.  
- Updated `.gitignore` to exclude PHPStan and PHP‑CS‑Fixer cache files.  
- Updated several JS files (`file‑preview.js`, `file‑upload‑queue.js`)
eand PHP controllers (`MediaController.php`, `SearchController.php`,
`SystemController.php`).  
- Minor adjustments to `TODO.md`, `app/src/Database.php`,
`app/src/Parsedown.php`, `app/src/ShareLink.php`, and
`app/src/SmtpRelay.php`.

.php-cs-fixer.dist.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+use PhpCsFixer\Config;
+use PhpCsFixer\Finder;
+
+return (new Config())
+    ->setRiskyAllowed(false)
+    ->setRules([
+        '@PSR12' => true,
+        '@PHP80Migration' => true,
+        'array_syntax' => ['syntax' => 'short'],
+        'no_unused_imports' => true,
+        'ordered_imports' => ['sort_algorithm' => 'alpha'],
+        'single_quote' => true,
+        'trailing_comma_in_multiline' => true,
+    ])
+    ->setFinder(
+        (new Finder())
+            ->in(__DIR__ . '/app/src')
+            ->in(__DIR__ . '/app/tests')
+            ->name('*.php')
+    )
+;