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`.

phpstan-baseline.neon

@@ -0,0 +1,55 @@
+parameters:
+	ignoreErrors:
+		-
+			message: '#^Property SearchController\:\:\$rateLimit is never read, only written\.$#'
+			identifier: property.onlyWritten
+			count: 1
+			path: app/src/Controllers/SearchController.php
+
+		-
+			message: '#^Strict comparison using \!\=\= between mixed~\(0\|0\.0\|''''\|''0''\|array\{\}\|false\|null\) and '''' will always evaluate to true\.$#'
+			identifier: notIdentical.alwaysTrue
+			count: 1
+			path: app/src/Database.php
+
+		-
+			message: '#^Property Dispatcher\:\:\$queryParams is never read, only written\.$#'
+			identifier: property.onlyWritten
+			count: 1
+			path: app/src/Dispatcher.php
+
+		-
+			message: '#^Unsafe usage of new static\(\)\.$#'
+			identifier: new.static
+			count: 1
+			path: app/src/Parsedown.php
+
+		-
+			message: '#^Variable \$text might not be defined\.$#'
+			identifier: variable.undefined
+			count: 2
+			path: app/src/Parsedown.php
+
+		-
+			message: '#^Offset ''from_email'' on array\{host\: string, port\: int, encryption\: string, username\: string, password\: string, from_email\: string, from_name\: string, notify_email\: string\} on left side of \?\? always exists and is not nullable\.$#'
+			identifier: nullCoalesce.offset
+			count: 1
+			path: app/src/SmtpRelay.php
+
+		-
+			message: '#^Offset ''from_name'' on array\{host\: string, port\: int, encryption\: string, username\: string, password\: string, from_email\: non\-empty\-string, from_name\: string, notify_email\: string\} on left side of \?\? always exists and is not nullable\.$#'
+			identifier: nullCoalesce.offset
+			count: 1
+			path: app/src/SmtpRelay.php
+
+		-
+			message: '#^Offset ''notify_email'' on array\{host\: string, port\: int, encryption\: string, username\: string, password\: string, from_email\: string, from_name\: string, notify_email\: string\} on left side of \?\? always exists and is not nullable\.$#'
+			identifier: nullCoalesce.offset
+			count: 1
+			path: app/src/SmtpRelay.php
+
+		-
+			message: '#^Static method SmtpRelay\:\:htmlToPlain\(\) is unused\.$#'
+			identifier: method.unused
+			count: 1
+			path: app/src/SmtpRelay.php