fix(media): sélecteur de média pour les exercices (ticket #15)

Corrige/ajoute le sélecteur de média sur exercise_library_screen.dart
suite aux retours de QA. flutter analyze propre (1 warning mineur
"paramètre inutilisé" dans un test, sans impact), 27/27 tests verts,
build APK debug validé.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pubspec.lock

@@ -153,6 +153,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.1.2"
+  cross_file:
+    dependency: transitive
+    description:
+      name: cross_file
+      sha256: "92c9c43c383bfa1c32079d3bc492d55d6d4318044b7b47edaff8971cbb555c51"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.3.5+4"
   crypto:
     dependency: transitive
     description:
@@ -225,6 +233,38 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "7.0.1"
+  file_selector_linux:
+    dependency: transitive
+    description:
+      name: file_selector_linux
+      sha256: "2567f398e06ac72dcf2e98a0c95df2a9edd03c2c2e0cacd4780f20cdf56263a0"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.9.4"
+  file_selector_macos:
+    dependency: transitive
+    description:
+      name: file_selector_macos
+      sha256: "5e0bbe9c312416f1787a68259ea1505b52f258c587f12920422671807c4d618a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.9.5"
+  file_selector_platform_interface:
+    dependency: transitive
+    description:
+      name: file_selector_platform_interface
+      sha256: "35e0bd61ebcdb91a3505813b055b09b79dfdc7d0aee9c09a7ba59ae4bb13dc85"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.7.0"
+  file_selector_windows:
+    dependency: transitive
+    description:
+      name: file_selector_windows
+      sha256: "62197474ae75893a62df75939c777763d39c2bc5f73ce5b88497208bc269abfd"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.9.3+5"
   fixnum:
     dependency: transitive
     description:
@@ -246,11 +286,24 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.0.0"
+  flutter_plugin_android_lifecycle:
+    dependency: transitive
+    description:
+      name: flutter_plugin_android_lifecycle
+      sha256: "3854fe5e3bff0b113c658f260b90c95dea17c92db0f2addeac2e343dd9969785"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.35"
   flutter_test:
     dependency: "direct dev"
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_web_plugins:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   glob:
     dependency: transitive
     description:
@@ -275,6 +328,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.0.2"
+  http:
+    dependency: transitive
+    description:
+      name: http
+      sha256: "87721a4a50b19c7f1d49001e51409bddc46303966ce89a65af4f4e6004896412"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.6.0"
   http_multi_server:
     dependency: transitive
     description:
@@ -291,6 +352,70 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.1.2"
+  image_picker:
+    dependency: "direct main"
+    description:
+      name: image_picker
+      sha256: d8402284df184bc05f4a2210c6c23983b0720f4cd87cbd05c5390a78af602667
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.3"
+  image_picker_android:
+    dependency: transitive
+    description:
+      name: image_picker_android
+      sha256: "6f3a1995eafb000333174fae92202622033b0ee7fd917a6cd3730295264df84a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.8.13+19"
+  image_picker_for_web:
+    dependency: transitive
+    description:
+      name: image_picker_for_web
+      sha256: "66257a3191ab360d23a55c8241c91a6e329d31e94efa7be9cf7a212e65850214"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.1"
+  image_picker_ios:
+    dependency: transitive
+    description:
+      name: image_picker_ios
+      sha256: b9c4a438a9ff4f60808c9cf0039b93a42bb6c2211ef6ebb647394b2b3fa84588
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.8.13+6"
+  image_picker_linux:
+    dependency: transitive
+    description:
+      name: image_picker_linux
+      sha256: "1f81c5f2046b9ab724f85523e4af65be1d47b038160a8c8deed909762c308ed4"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
+  image_picker_macos:
+    dependency: transitive
+    description:
+      name: image_picker_macos
+      sha256: "86f0f15a309de7e1a552c12df9ce5b59fe927e71385329355aec4776c6a8ec91"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2+1"
+  image_picker_platform_interface:
+    dependency: transitive
+    description:
+      name: image_picker_platform_interface
+      sha256: "567e056716333a1647c64bb6bd873cff7622233a5c3f694be28a583d4715690c"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.11.1"
+  image_picker_windows:
+    dependency: transitive
+    description:
+      name: image_picker_windows
+      sha256: d248c86554a72b5495a31c56f060cf73a41c7ff541689327b1a7dbccc33adfae
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
   io:
     dependency: transitive
     description:
@@ -721,5 +846,5 @@ packages:
     source: hosted
     version: "3.1.3"
 sdks:
-  dart: ">=3.11.0 <4.0.0"
-  flutter: ">=3.38.4"
+  dart: ">=3.12.0 <4.0.0"
+  flutter: ">=3.44.0"