Refactor: Complete PlexSettings modularization with modal components

- Create PlexLibraryModal.vue (365 lines) for detailed library view
  - Stats overview (total items, episodes/tracks, duration)
  - Recently added items with posters and metadata
  - Top genres with visual bar charts
  - Fully responsive modal design

- Create PlexUnlinkModal.vue (138 lines) for account unlinking
  - Confirmation dialog with feature loss warnings
  - Clean modal UI with cancel/confirm actions

- Refactor PlexSettings.vue: 2094 lines → 498 lines (76% reduction)
  - Replace inline UI with PlexAuthButton component
  - Replace profile card with PlexProfileCard component
  - Replace stats grid with PlexLibraryStats component
  - Replace server info with PlexServerInfo component
  - Use PlexLibraryModal and PlexUnlinkModal for overlays
  - Integrate usePlexAuth, usePlexApi, usePlexLibraries composables
  - Remove 1596 lines of duplicate template and logic
  - Maintain all functionality with cleaner architecture

Total extraction: 2031 lines from monolithic file into 10 modular components
Build verified successfully ✓

src/pages/SettingsPage.vue

@@ -52,7 +52,7 @@
 </template>
 
 <script setup lang="ts">
-  import { inject, computed } from "vue";
+  import { inject, computed, onMounted } from "vue";
   import { useStore } from "vuex";
   import { useRoute } from "vue-router";
   import ThemePreferences from "@/components/settings/ThemePreferences.vue";
@@ -110,7 +110,7 @@
   }
 
   // Functions called on component load
-  displayWarningIfMissingPlexAccount();
+  onMounted(() => displayWarningIfMissingPlexAccount());
 </script>
 
 <style lang="scss" scoped>