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/tests/Unit/DatabaseTest.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * Database Connection Test
  * Tests basic database connectivity and query functionality
@@ -24,16 +25,16 @@ try {
     if ($count >= 0) {
         echo "✓ PASS: Found {$count} published theses\n\n";
     } else {
-        throw new Exception("Invalid count returned");
+        throw new Exception('Invalid count returned');
     }
 
     // Test 3: Get published theses
     echo "Test 3: Get Published Theses\n";
     $theses = $db->getPublishedTheses(5, 0);
     if (is_array($theses)) {
-        echo "✓ PASS: Retrieved " . count($theses) . " theses\n\n";
+        echo '✓ PASS: Retrieved ' . count($theses) . " theses\n\n";
     } else {
-        throw new Exception("Invalid theses array returned");
+        throw new Exception('Invalid theses array returned');
     }
 
     // Test 4: Get single thesis (if any exist)
@@ -41,14 +42,14 @@ try {
         echo "Test 4: Get Single Thesis\n";
         $first = $theses[0];
         $thesis = $db->getThesisById($first['id']);
-        
+
         if ($thesis && isset($thesis['id'])) {
             echo "✓ PASS: Successfully retrieved thesis #{$first['id']}\n";
-            echo "  Title: " . $thesis['title'] . "\n";
-            echo "  Author(s): " . ($thesis['authors'] ?? 'N/A') . "\n";
-            echo "  Year: " . $thesis['year'] . "\n\n";
+            echo '  Title: ' . $thesis['title'] . "\n";
+            echo '  Author(s): ' . ($thesis['authors'] ?? 'N/A') . "\n";
+            echo '  Year: ' . $thesis['year'] . "\n\n";
         } else {
-            throw new Exception("Failed to retrieve thesis by ID");
+            throw new Exception('Failed to retrieve thesis by ID');
         }
     }
 
@@ -69,15 +70,15 @@ try {
     echo "Test 6: getUsedTags returns name column\n";
     $tags = $db->getUsedTags();
     if (is_array($tags) && (empty($tags) || isset($tags[0]['name']))) {
-        echo "✓ PASS: getUsedTags returned " . count($tags) . " tags with 'name' column\n\n";
+        echo '✓ PASS: getUsedTags returned ' . count($tags) . " tags with 'name' column\n\n";
     } else {
-        throw new Exception("getUsedTags did not return expected structure: " . json_encode($tags[0] ?? []));
+        throw new Exception('getUsedTags did not return expected structure: ' . json_encode($tags[0] ?? []));
     }
 
     echo "✅ All database tests passed!\n";
     return true;
 
 } catch (Exception $e) {
-    echo "❌ FAIL: " . $e->getMessage() . "\n";
+    echo '❌ FAIL: ' . $e->getMessage() . "\n";
     return false;
 }

app/tests/Unit/RateLimitTest.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * Rate Limit Test
  * Tests rate limiting functionality
@@ -19,9 +20,9 @@ try {
     echo "Test 2: Check Method\n";
     $allowed = $rateLimit->check();
     if (is_bool($allowed)) {
-        echo "✓ PASS: check() returns boolean (allowed: " . ($allowed ? 'yes' : 'no') . ")\n\n";
+        echo '✓ PASS: check() returns boolean (allowed: ' . ($allowed ? 'yes' : 'no') . ")\n\n";
     } else {
-        throw new Exception("check() did not return boolean");
+        throw new Exception('check() did not return boolean');
     }
 
     // Test 3: Headers method
@@ -37,7 +38,7 @@ try {
     if (is_int($resetTime) && $resetTime >= 0) {
         echo "✓ PASS: getResetTime() returns valid value ($resetTime seconds)\n\n";
     } else {
-        throw new Exception("Invalid reset time");
+        throw new Exception('Invalid reset time');
     }
 
     // Test 5: Cleanup method
@@ -49,6 +50,6 @@ try {
     return true;
 
 } catch (Exception $e) {
-    echo "❌ FAIL: " . $e->getMessage() . "\n";
+    echo '❌ FAIL: ' . $e->getMessage() . "\n";
     return false;
 }