fix: batch backfill validation skip logs into single summary event

Instead of emitting one log per invalid record during backfill, collect
counts by collection and emit a single validation_skips event per repo.

Co-Authored-By: Claude Opus 4.6 <[e-mail]>

packages/hatk/src/backfill.ts

···
     // Insert records in chunks to limit memory usage
     const CHUNK_SIZE = 1000
     let chunk: BulkRecord[] = []
+    const validationSkips: Record<string, number> = {}
     for (const entry of entries) {
       const collection = entry.path.split('/')[0]
       if (!collections.has(collection)) continue
···
 
         const validationError = validateRecord(getLexiconArray(), collection, record)
         if (validationError) {
-          emit('backfill', 'validation_skip', {
-            uri,
-            collection,
-            path: validationError.path,
-            error: validationError.message,
-          })
+          validationSkips[collection] = (validationSkips[collection] || 0) + 1
           continue
         }
 
···
     }
     if (chunk.length > 0) {
       count += await bulkInsertRecords(chunk)
+    }
+    const totalSkips = Object.values(validationSkips).reduce((a, b) => a + b, 0)
+    if (totalSkips > 0) {
+      emit('backfill', 'validation_skips', { did, total: totalSkips, by_collection: validationSkips })
     }
     await setRepoStatus(did, 'active', commit.rev, { handle })
     return count