Implement Linux data models (C/Vala)

- Add FeedItem, Feed, FeedSubscription models
- Add SearchResult, SearchFilters, SearchQuery models
- Add NotificationPreferences, ReadingPreferences models
- Implement JSON serialization/deserialization for all models
- Add equality comparison methods
- Following GNOME HIG naming conventions
- Build system configured with Meson/Ninja

native-route/linux/meson.build

@@ -0,0 +1,33 @@
+project('rssuper-linux', 'vala', 'c',
+  version: '0.1.0',
+  default_options: [
+    'c_std=c11',
+    'warning_level=3',
+    'werror=false',
+  ]
+)
+
+vala = find_program('valac')
+meson_version_check = run_command(vala, '--version', check: true)
+
+# Dependencies
+glib_dep = dependency('glib-2.0', version: '>= 2.58')
+gio_dep = dependency('gio-2.0', version: '>= 2.58')
+json_dep = dependency('json-glib-1.0', version: '>= 1.4')
+
+# Source files
+models = files(
+  'src/models/feed-item.vala',
+  'src/models/feed.vala',
+  'src/models/feed-subscription.vala',
+  'src/models/search-result.vala',
+  'src/models/search-filters.vala',
+  'src/models/notification-preferences.vala',
+  'src/models/reading-preferences.vala',
+)
+
+# Main library
+models_lib = library('rssuper-models', models,
+  dependencies: [glib_dep, gio_dep, json_dep],
+  install: false
+)