fix(critical): enable metadata indexing in write-only mode + force buffering activation

🚨 CRITICAL FIXES:

1. METADATA INDEXING IN WRITE-ONLY MODE:
   - Was: if (\!this.writeOnly) - DISABLED metadata indexing for bluesky/github packages\!
   - Now: if (\!this.readOnly) - ENABLES metadata indexing in write-only mode
   - Fixes all conditional checks to allow write-only mode indexing
   - Write-only mode NEEDS metadata indices for search capability\!

2. STATISTICS FOLDER LOCATION:
   - Statistics now go to _system/ folder instead of legacy _index/
   - Uses systemPrefix instead of indexPrefix for new statistics

3. FORCE BUFFERING ACTIVATION:
   - Threshold lowered from 1 to 0 (immediate activation)
   - Added 'true' condition to force enable high-volume mode
   - This should guarantee buffering activation in production

IMPACT:
- bluesky-package and github-package will now CREATE metadata indices
- _metadata/noun/ and _metadata/verb/ folders will appear in S3
- Metadata filtering and field searches will work in write-only mode
- Statistics will be in proper _system/ folder structure
- Buffering should activate immediately (guaranteed)

This fixes the missing S3 folder structure and search capabilities.

src/brainyData.ts

@@ -1428,8 +1428,9 @@ export class BrainyData<T = any> implements BrainyDataInterface<T> {
         // Ignore errors loading existing statistics
       }
 
-      // Initialize metadata index if not in write-only mode
-      if (!this.writeOnly) {
+      // Initialize metadata index unless in read-only mode
+      // Write-only mode NEEDS metadata indexing for search capability!
+      if (!this.readOnly) {
         this.metadataIndex = new MetadataIndexManager(
           this.storage!,
           this.config.metadataIndex
@@ -1909,8 +1910,8 @@ export class BrainyData<T = any> implements BrainyDataInterface<T> {
 
           await this.storage!.saveMetadata(id, metadataToSave)
 
-          // Update metadata index
-          if (this.metadataIndex && !this.readOnly && !this.frozen) {
+          // Update metadata index (write-only mode should build indices!)
+          if (this.metadataIndex && !this.frozen) {
             await this.metadataIndex.addToIndex(id, metadataToSave)
           }
 
@@ -3362,8 +3363,8 @@ export class BrainyData<T = any> implements BrainyDataInterface<T> {
         // Get metadata before removing for index cleanup
         const existingMetadata = await this.storage!.getMetadata(actualId)
         
-        // Remove from metadata index
-        if (this.metadataIndex && existingMetadata && !this.readOnly && !this.frozen) {
+        // Remove from metadata index (write-only mode should update indices!)
+        if (this.metadataIndex && existingMetadata && !this.frozen) {
           await this.metadataIndex.removeFromIndex(actualId, existingMetadata)
         }
         
@@ -3478,8 +3479,8 @@ export class BrainyData<T = any> implements BrainyDataInterface<T> {
       // Update metadata
       await this.storage!.saveMetadata(id, metadata)
 
-      // Update metadata index
-      if (this.metadataIndex && !this.readOnly && !this.frozen) {
+      // Update metadata index (write-only mode should build indices!)
+      if (this.metadataIndex && !this.frozen) {
         // Remove old metadata from index if it exists
         const oldMetadata = await this.storage!.getMetadata(id)
         if (oldMetadata) {