feat(time-tracking) : add ActiveTimeEntryProvider, fixtures, and serialization groups

- ActiveTimeEntryProvider returns active timer for current user
- TimeEntry fixtures with 10 sample entries for the SIRH project
- Add time_entry:read group to Project, User, and TaskType for embedded serialization

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Entity/User.php

@@ -46,11 +46,11 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
     #[ORM\Id]
     #[ORM\GeneratedValue]
     #[ORM\Column]
-    #[Groups(['me:read', 'task:read', 'user:list'])]
+    #[Groups(['me:read', 'task:read', 'user:list', 'time_entry:read'])]
     private ?int $id = null;
 
     #[ORM\Column(length: 180, unique: true)]
-    #[Groups(['me:read', 'task:read', 'user:list', 'user:write'])]
+    #[Groups(['me:read', 'task:read', 'user:list', 'user:write', 'time_entry:read'])]
     private ?string $username = null;
 
     /** @var list<string> */