refactor(content): add loading state to edit source dropdowns

Refactors the edit source page to conditionally disable the language and country dropdowns while their respective full lists are being fetched in the background.

This aligns the UI behavior with the create/edit headline pages and the create source page, providing a better user experience by preventing interaction with incomplete data.

Author: fulleni

lib/content_management/view/edit_source_page.dart

@@ -198,24 +198,36 @@ class _EditSourceViewState extends State<_EditSourceView> {
                       ),
                     ),
                     const SizedBox(height: AppSpacing.lg),
-                    DropdownButtonFormField<Language?>(
-                      value: state.language,
-                      decoration: InputDecoration(
-                        labelText: l10n.language,
-                        border: const OutlineInputBorder(),
-                      ),
-                      items: [
-                        DropdownMenuItem(value: null, child: Text(l10n.none)),
-                        ...state.languages.map(
-                          (language) => DropdownMenuItem(
-                            value: language,
-                            child: Text(language.name),
+                    BlocBuilder<ContentManagementBloc, ContentManagementState>(
+                      builder: (context, contentState) {
+                        final isLoading = contentState.allLanguagesStatus ==
+                            ContentManagementStatus.loading;
+                        return DropdownButtonFormField<Language?>(
+                          value: state.language,
+                          decoration: InputDecoration(
+                            labelText: l10n.language,
+                            border: const OutlineInputBorder(),
+                            helperText:
+                                isLoading ? l10n.loadingFullList : null,
                           ),
-                        ),
-                      ],
-                      onChanged: (value) => context.read<EditSourceBloc>().add(
-                        EditSourceLanguageChanged(value),
-                      ),
+                          items: [
+                            DropdownMenuItem(
+                                value: null, child: Text(l10n.none)),
+                            ...state.languages.map(
+                              (language) => DropdownMenuItem(
+                                value: language,
+                                child: Text(language.name),
+                              ),
+                            ),
+                          ],
+                          onChanged: isLoading
+                              ? null
+                              : (value) =>
+                                  context.read<EditSourceBloc>().add(
+                                    EditSourceLanguageChanged(value),
+                                  ),
+                        );
+                      },
                     ),
                     const SizedBox(height: AppSpacing.lg),
                     DropdownButtonFormField<SourceType?>(
@@ -238,40 +250,52 @@ class _EditSourceViewState extends State<_EditSourceView> {
                       ),
                     ),
                     const SizedBox(height: AppSpacing.lg),
-                    DropdownButtonFormField<Country?>(
-                      value: state.headquarters,
-                      decoration: InputDecoration(
-                        labelText: l10n.headquarters,
-                        border: const OutlineInputBorder(),
-                      ),
-                      items: [
-                        DropdownMenuItem(value: null, child: Text(l10n.none)),
-                        ...state.countries.map(
-                          (country) => DropdownMenuItem(
-                            value: country,
-                            child: Row(
-                              children: [
-                                SizedBox(
-                                  width: 32,
-                                  height: 20,
-                                  child: Image.network(
-                                    country.flagUrl,
-                                    fit: BoxFit.cover,
-                                    errorBuilder:
-                                        (context, error, stackTrace) =>
-                                            const Icon(Icons.flag),
-                                  ),
+                    BlocBuilder<ContentManagementBloc, ContentManagementState>(
+                      builder: (context, contentState) {
+                        final isLoading = contentState.allCountriesStatus ==
+                            ContentManagementStatus.loading;
+                        return DropdownButtonFormField<Country?>(
+                          value: state.headquarters,
+                          decoration: InputDecoration(
+                            labelText: l10n.headquarters,
+                            border: const OutlineInputBorder(),
+                            helperText:
+                                isLoading ? l10n.loadingFullList : null,
+                          ),
+                          items: [
+                            DropdownMenuItem(
+                                value: null, child: Text(l10n.none)),
+                            ...state.countries.map(
+                              (country) => DropdownMenuItem(
+                                value: country,
+                                child: Row(
+                                  children: [
+                                    SizedBox(
+                                      width: 32,
+                                      height: 20,
+                                      child: Image.network(
+                                        country.flagUrl,
+                                        fit: BoxFit.cover,
+                                        errorBuilder:
+                                            (context, error, stackTrace) =>
+                                                const Icon(Icons.flag),
+                                      ),
+                                    ),
+                                    const SizedBox(width: AppSpacing.md),
+                                    Text(country.name),
+                                  ],
                                 ),
-                                const SizedBox(width: AppSpacing.md),
-                                Text(country.name),
-                              ],
+                              ),
                             ),
-                          ),
-                        ),
-                      ],
-                      onChanged: (value) => context.read<EditSourceBloc>().add(
-                        EditSourceHeadquartersChanged(value),
-                      ),
+                          ],
+                          onChanged: isLoading
+                              ? null
+                              : (value) =>
+                                  context.read<EditSourceBloc>().add(
+                                    EditSourceHeadquartersChanged(value),
+                                  ),
+                        );
+                      },
                     ),
                     const SizedBox(height: AppSpacing.lg),
                     DropdownButtonFormField<ContentStatus>(