feat: add real-time files watch for LibraryView

Implement comprehensive monitoring system:
- Watch for new registered files (5s interval)
- Detect file status changes (registered → processing → completed)
- Monitor file additions/removals

Functions added:
- startFilesWatch(): Poll get_files API every 5s
- stopFilesWatch(): Clean up interval

LibraryView integration:
- Enable on mount
- Disable on unmount

Enables cross-machine monitoring: one operates, another watches changes

src/store.ts

@@ -352,6 +352,7 @@ const loadingFileStats = new Set<string>()
 
 let statsRefreshInterval: ReturnType<typeof setInterval> | null = null
 let processingPollInterval: ReturnType<typeof setInterval> | null = null
+let filesWatchInterval: ReturnType<typeof setInterval> | null = null
 
 export function startStatsAutoRefresh() {
   if (statsRefreshInterval) return
@@ -389,6 +390,50 @@ export function stopProcessingFilesPolling() {
   }
 }
 
+export function startFilesWatch() {
+  if (filesWatchInterval) return
+  filesWatchInterval = setInterval(async () => {
+    try {
+      const result = await apiCall('get_files', { args: { pageSize: 500 } })
+      const newFiles = Array.isArray(result) ? result : []
+      
+      // Check for new files
+      const oldUuids = new Set(filesCache.value.map((f: any) => f.file_uuid).filter(Boolean))
+      const newUuids = newFiles.map((f: any) => f.file_uuid).filter(Boolean)
+      
+      // Detect new registered files
+      const added = newUuids.filter((uuid: string) => !oldUuids.has(uuid))
+      const removed = Array.from(oldUuids).filter((uuid: string) => !newUuids.includes(uuid))
+      
+      if (added.length > 0 || removed.length > 0) {
+        filesCache.value = newFiles
+      }
+      
+      // Check status changes for existing files
+      for (const newFile of newFiles) {
+        if (!newFile.file_uuid) continue
+        const oldFile = filesCache.value.find((f: any) => f.file_uuid === newFile.file_uuid)
+        if (oldFile && oldFile.status !== newFile.status) {
+          // Status changed, update cache
+          const idx = filesCache.value.findIndex((f: any) => f.file_uuid === newFile.file_uuid)
+          if (idx >= 0) {
+            filesCache.value[idx] = newFile
+          }
+        }
+      }
+    } catch (e) {
+      console.error('[startFilesWatch] Error:', e)
+    }
+  }, 5000)
+}
+
+export function stopFilesWatch() {
+  if (filesWatchInterval) {
+    clearInterval(filesWatchInterval)
+    filesWatchInterval = null
+  }
+}
+
 function drainThumbQueue() {
   if (activeThumbLoads >= MAX_CONCURRENT || thumbQueue.length === 0) return
   activeThumbLoads++