refactor : simplify codebase and fix critical issues

Backend:
- Add MCP Serializer to centralize entity-to-array conversion (~300 lines deduped)
- Fix race condition in task/ticket number generation (SELECT FOR UPDATE + transaction)
- Add unique constraint on task (project_id, number) with migration
- Fix MIME type validation: use server-detected finfo instead of client-supplied type
- Add allowlist of permitted MIME types for uploads
- Fix TaskDocumentDownloadController: allow ROLE_CLIENT access, add priority:1
- Fix notification sent even when ticket status unchanged
- Remove redundant exception constructors
- Simplify services (BookStackApi double fetch, TokenEncryptor, GiteaApi)
- Consolidate duplicate checks in processors

Frontend:
- Fix useApi isHandlingUnauthorized scope (module-level to prevent double 401 redirect)
- Fix client-tickets toast key copy-paste bug
- Merge duplicated tasks service methods (getByProject + getByProjectArchived)
- Extract shared uploadWithRelation helper in task-documents service
- Extract formatFileSize utility from duplicated component code
- Extract status transition logic into useClientTicketHelpers composable
- Remove dead code (unused router, handleLogout, empty script blocks)
- Merge duplicate watchers and onMounted calls
- Normalize arrow functions to function declarations per convention

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Service/TokenEncryptor.php

@@ -17,31 +17,10 @@ final class TokenEncryptor
         #[Autowire('%env(ENCRYPTION_KEY)%')]
         string $encryptionKey,
     ) {
-        if ('' === $encryptionKey) {
-            $this->key        = '';
-            $this->configured = false;
+        $key = $this->tryDecodeKey($encryptionKey);
 
-            return;
-        }
-
-        try {
-            $key = sodium_hex2bin($encryptionKey);
-        } catch (SodiumException) {
-            $this->key        = '';
-            $this->configured = false;
-
-            return;
-        }
-
-        if (SODIUM_CRYPTO_SECRETBOX_KEYBYTES !== mb_strlen($key, '8bit')) {
-            $this->key        = '';
-            $this->configured = false;
-
-            return;
-        }
-
-        $this->key        = $key;
-        $this->configured = true;
+        $this->key        = $key ?? '';
+        $this->configured = null !== $key;
     }
 
     public function encrypt(string $plaintext): string
@@ -71,6 +50,25 @@ final class TokenEncryptor
         return $plaintext;
     }
 
+    private function tryDecodeKey(string $encryptionKey): ?string
+    {
+        if ('' === $encryptionKey) {
+            return null;
+        }
+
+        try {
+            $key = sodium_hex2bin($encryptionKey);
+        } catch (SodiumException) {
+            return null;
+        }
+
+        if (SODIUM_CRYPTO_SECRETBOX_KEYBYTES !== mb_strlen($key, '8bit')) {
+            return null;
+        }
+
+        return $key;
+    }
+
     private function assertConfigured(): void
     {
         if (!$this->configured) {