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/services/readingDataProcessor.ts

@@ -0,0 +1,140 @@
+import { NostrEvent } from 'nostr-tools'
+import { ReadItem } from './readsService'
+
+const READING_POSITION_PREFIX = 'boris:reading-position:'
+
+interface ReadArticle {
+  id: string
+  url?: string
+  eventId?: string
+  eventKind?: number
+  markedAt: number
+}
+
+/**
+ * Processes reading position events into ReadItems
+ */
+export function processReadingPositions(
+  events: NostrEvent[],
+  readsMap: Map<string, ReadItem>
+): void {
+  for (const event of events) {
+    const dTag = event.tags.find(t => t[0] === 'd')?.[1]
+    if (!dTag || !dTag.startsWith(READING_POSITION_PREFIX)) continue
+
+    const identifier = dTag.replace(READING_POSITION_PREFIX, '')
+    
+    try {
+      const positionData = JSON.parse(event.content)
+      const position = positionData.position
+      const timestamp = positionData.timestamp
+
+      let itemId: string
+      let itemUrl: string | undefined
+      let itemType: 'article' | 'external' = 'external'
+
+      // Check if it's a nostr article (naddr format)
+      if (identifier.startsWith('naddr1')) {
+        itemId = identifier
+        itemType = 'article'
+      } else {
+        // It's a base64url-encoded URL
+        try {
+          itemUrl = atob(identifier.replace(/-/g, '+').replace(/_/g, '/'))
+          itemId = itemUrl
+          itemType = 'external'
+        } catch (e) {
+          console.warn('Failed to decode URL identifier:', identifier)
+          continue
+        }
+      }
+
+      // Add or update the item
+      const existing = readsMap.get(itemId)
+      if (!existing || !existing.readingTimestamp || timestamp > existing.readingTimestamp) {
+        readsMap.set(itemId, {
+          ...existing,
+          id: itemId,
+          source: 'reading-progress',
+          type: itemType,
+          url: itemUrl,
+          readingProgress: position,
+          readingTimestamp: timestamp
+        })
+      }
+    } catch (error) {
+      console.warn('Failed to parse reading position:', error)
+    }
+  }
+}
+
+/**
+ * Processes marked-as-read articles into ReadItems
+ */
+export function processMarkedAsRead(
+  articles: ReadArticle[],
+  readsMap: Map<string, ReadItem>
+): void {
+  for (const article of articles) {
+    const existing = readsMap.get(article.id)
+    
+    if (article.eventId && article.eventKind === 30023) {
+      // Nostr article
+      readsMap.set(article.id, {
+        ...existing,
+        id: article.id,
+        source: 'marked-as-read',
+        type: 'article',
+        markedAsRead: true,
+        markedAt: article.markedAt,
+        readingTimestamp: existing?.readingTimestamp || article.markedAt
+      })
+    } else if (article.url) {
+      // External URL
+      readsMap.set(article.id, {
+        ...existing,
+        id: article.id,
+        source: 'marked-as-read',
+        type: 'external',
+        url: article.url,
+        markedAsRead: true,
+        markedAt: article.markedAt,
+        readingTimestamp: existing?.readingTimestamp || article.markedAt
+      })
+    }
+  }
+}
+
+/**
+ * Sorts ReadItems by most recent reading activity
+ */
+export function sortByReadingActivity(items: ReadItem[]): ReadItem[] {
+  return items.sort((a, b) => {
+    const timeA = a.readingTimestamp || a.markedAt || 0
+    const timeB = b.readingTimestamp || b.markedAt || 0
+    return timeB - timeA
+  })
+}
+
+/**
+ * Filters out items without timestamps or proper titles
+ */
+export function filterValidItems(items: ReadItem[]): ReadItem[] {
+  return items.filter(item => {
+    // Only include items that have a timestamp
+    const hasTimestamp = (item.readingTimestamp && item.readingTimestamp > 0) || 
+                        (item.markedAt && item.markedAt > 0)
+    if (!hasTimestamp) return false
+    
+    // Filter out items without titles
+    if (!item.title || item.title === 'Untitled') {
+      // For Nostr articles, we need the title from the event
+      if (item.type === 'article' && !item.event) return false
+      // For external URLs, we need a proper title
+      if (item.type === 'external' && !item.title) return false
+    }
+    
+    return true
+  })
+}
+