feat: prevent duplicate TFE submissions with logging and user feedback

- Add DuplicateThesisException (typed, carries existing thesis metadata)
- Add Database::findDuplicateThesis(): matches on year + author + normalised
  title (exact, prefix, Levenshtein ≤10% of longer string)
- ThesisCreateController::submit() runs duplicate check before any DB write
  and throws DuplicateThesisException on match
- AppLogger::logDuplicate() writes status=duplicate entries to the JSON-lines
  log for audit purposes
- App::flash/consumeFlash extended to support 'warning' flash type
- admin/actions/formulaire.php: catches DuplicateThesisException, logs it,
  flashes an HTML warning toast with a clickable link to the existing thesis,
  and repopulates the form fields
- partage/index.php: same catch block; surfaces a plain-text flash-warning
  banner on the student form with identifier, title, and year of the match;
  form is repopulated via session
- toast.php: renders toast--warning variant
- admin.css: .toast--warning + link colour rules
- form.css: .flash-warning style for the partage form

app/src/ShareLink.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * ShareLink — model for student-access share links.
  *
@@ -58,8 +59,8 @@ class ShareLink
             : null;
 
         $stmt = $this->db->getConnection()->prepare(
-            "INSERT INTO share_links (slug, objet_restriction, password_hash, is_active, created_by, expires_at)
-             VALUES (?, ?, ?, 1, ?, ?)"
+            'INSERT INTO share_links (slug, objet_restriction, password_hash, is_active, created_by, expires_at)
+             VALUES (?, ?, ?, 1, ?, ?)'
         );
         $stmt->execute([$slug, $objetRestriction, $passwordHash, $createdBy, $expiresAt]);
 
@@ -74,7 +75,7 @@ class ShareLink
     public function findBySlug(string $slug): ?array
     {
         $stmt = $this->db->getConnection()->prepare(
-            "SELECT * FROM share_links WHERE slug = ?"
+            'SELECT * FROM share_links WHERE slug = ?'
         );
         $stmt->execute([$slug]);
         $row = $stmt->fetch();
@@ -89,7 +90,7 @@ class ShareLink
     public function findById(int $id): ?array
     {
         $stmt = $this->db->getConnection()->prepare(
-            "SELECT * FROM share_links WHERE id = ?"
+            'SELECT * FROM share_links WHERE id = ?'
         );
         $stmt->execute([$id]);
         $row = $stmt->fetch();
@@ -104,7 +105,7 @@ class ShareLink
     public function listAll(): array
     {
         $stmt = $this->db->getConnection()->query(
-            "SELECT * FROM share_links ORDER BY created_at DESC"
+            'SELECT * FROM share_links ORDER BY created_at DESC'
         );
         return $stmt->fetchAll();
     }
@@ -115,7 +116,7 @@ class ShareLink
     public function toggleActive(int $id): void
     {
         $this->db->getConnection()->prepare(
-            "UPDATE share_links SET is_active = NOT is_active WHERE id = ?"
+            'UPDATE share_links SET is_active = NOT is_active WHERE id = ?'
         )->execute([$id]);
     }
 
@@ -128,7 +129,7 @@ class ShareLink
     {
         $hash = $password !== null ? password_hash($password, PASSWORD_BCRYPT) : null;
         $this->db->getConnection()->prepare(
-            "UPDATE share_links SET password_hash = ? WHERE id = ?"
+            'UPDATE share_links SET password_hash = ? WHERE id = ?'
         )->execute([$hash, $id]);
     }
 
@@ -138,7 +139,7 @@ class ShareLink
     public function delete(int $id): void
     {
         $this->db->getConnection()->prepare(
-            "DELETE FROM share_links WHERE id = ?"
+            'DELETE FROM share_links WHERE id = ?'
         )->execute([$id]);
     }
 
@@ -148,7 +149,7 @@ class ShareLink
     public function incrementUsage(int $id): void
     {
         $this->db->getConnection()->prepare(
-            "UPDATE share_links SET usage_count = usage_count + 1 WHERE id = ?"
+            'UPDATE share_links SET usage_count = usage_count + 1 WHERE id = ?'
         )->execute([$id]);
     }