Convert AI tagging to background job with progress tracking

- Add TaggingJob model for tracking tagging progress
- Convert batch tagging to background job processing (prevents timeouts)
- Add real-time progress polling in UI with percentage/count display
- Add admin notifications when tagging job completes or fails
- Export getTaggingSettings and getAvailableTags functions

After deployment, run: npx prisma migrate deploy

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/server/services/ai-tagging.ts

@@ -94,7 +94,7 @@ Rules:
 /**
  * Get system settings for AI tagging
  */
-async function getTaggingSettings(): Promise<{
+export async function getTaggingSettings(): Promise<{
   enabled: boolean
   maxTags: number
 }> {
@@ -125,7 +125,7 @@ async function getTaggingSettings(): Promise<{
 /**
  * Get all active expertise tags
  */
-async function getAvailableTags(): Promise<AvailableTag[]> {
+export async function getAvailableTags(): Promise<AvailableTag[]> {
   return prisma.expertiseTag.findMany({
     where: { isActive: true },
     select: {