fix: per-sheet column detection in Excel importer

CRITICAL FIX for Entity_* placeholder names in multi-sheet Excel imports

Root Cause:
- Column detection ran globally on first row of all combined sheets
- Different sheets have different column structures (Term vs Name, etc.)
- Concepts sheet: [Term, Definition] → detected 'Term' column ✅
- Characters sheet: [Name, Description] → looked for 'Term' column ❌
- Result: Characters/Places/Other fell back to Entity_* placeholders

Fix:
- Group rows by sheet (_sheet field)
- Detect columns per-sheet, not globally
- Each sheet now uses its own column mapping
- Characters/Places sheets now correctly find 'Name' column

Impact:
- Concepts: Still work (no change)
- Characters/Places/Other: NOW USE ACTUAL NAMES! 🎉

Also removed debug logging from v4.8.5 (performance overhead)

Fixes: Workshop File Explorer showing Entity_* instead of real names
Ref: BRAINY_V4.8.4_VFS_UNDEFINED_NAMES_BUG.md

src/vfs/PathResolver.ts

@@ -230,7 +230,6 @@ export class PathResolver {
       from: dirId,
       type: VerbType.Contains
     })
-    console.log(`[DEBUG PathResolver] getChildren(${dirId}): Found ${relations.length} Contains relations`)
 
     const validChildren: VFSEntity[]= []
     const childNames = new Set<string>()
@@ -238,24 +237,12 @@ export class PathResolver {
     // Fetch all child entities via relationships
     for (const relation of relations) {
       const entity = await this.brain.get(relation.to)
-      console.log(`[DEBUG PathResolver] Retrieved entity ${relation.to}:`, {
-        exists: !!entity,
-        type: entity?.type,
-        hasMetadata: !!entity?.metadata,
-        metadataKeys: entity?.metadata ? Object.keys(entity.metadata) : [],
-        metadata_vfsType: entity?.metadata?.vfsType,
-        metadata_name: entity?.metadata?.name
-      })
-
       if (entity && entity.metadata?.vfsType && entity.metadata?.name) {
         validChildren.push(entity as VFSEntity)
         childNames.add(entity.metadata.name)
-      } else {
-        console.log(`[DEBUG PathResolver] ❌ FILTERED OUT entity ${relation.to} - missing vfsType or name`)
       }
     }
 
-    console.log(`[DEBUG PathResolver] Returning ${validChildren.length} valid children (filtered from ${relations.length})`)
     // Update cache
     this.parentCache.set(dirId, childNames)
     return validChildren