refactor: make code more DRY by extracting shared utilities

- Create readingProgressUtils.ts with filterByReadingProgress function
- Create readingDataProcessor.ts with shared processing functions:
  - processReadingPositions
  - processMarkedAsRead
  - filterValidItems
  - sortByReadingActivity
- Refactor readsService.ts to use shared utilities
- Refactor linksService.ts to use shared utilities
- Eliminate 100+ lines of duplicated code
- Simplify Me.tsx filter logic to 2 lines

Benefits:
- Single source of truth for reading progress filtering
- Easier to maintain and modify
- Less code duplication across services
- More testable with isolated utility functions

src/utils/readingProgressUtils.ts

@@ -0,0 +1,30 @@
+import { ReadItem } from '../services/readsService'
+import { ReadingProgressFilterType } from '../components/ReadingProgressFilters'
+
+/**
+ * Filters ReadItems by reading progress
+ */
+export function filterByReadingProgress(
+  items: ReadItem[],
+  filter: ReadingProgressFilterType
+): ReadItem[] {
+  return items.filter((item) => {
+    const progress = item.readingProgress || 0
+    const isMarked = item.markedAsRead || false
+    
+    switch (filter) {
+      case 'unopened':
+        return progress === 0 && !isMarked
+      case 'started':
+        return progress > 0 && progress <= 0.10 && !isMarked
+      case 'reading':
+        return progress > 0.10 && progress <= 0.94 && !isMarked
+      case 'completed':
+        return progress >= 0.95 || isMarked
+      case 'all':
+      default:
+        return true
+    }
+  })
+}
+