Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/utils/fileHistoryUtils.ts

@@ -0,0 +1,78 @@
+/**
+ * File History Utilities
+ *
+ * Helper functions for IndexedDB-based file history management.
+ * Handles file history operations and lineage tracking.
+ */
+import { StirlingFileStub } from '@app/types/fileContext';
+
+/**
+ * Group files by processing branches - each branch ends in a leaf file
+ * Returns Map<fileId, lineagePath[]> where fileId is the leaf and lineagePath is the path back to original
+ */
+export function groupFilesByOriginal(StirlingFileStubs: StirlingFileStub[]): Map<string, StirlingFileStub[]> {
+  const groups = new Map<string, StirlingFileStub[]>();
+
+  // Create a map for quick lookups
+  const fileMap = new Map<string, StirlingFileStub>();
+  for (const record of StirlingFileStubs) {
+    fileMap.set(record.id, record);
+  }
+
+  // Find leaf files (files that are not parents of any other files AND have version history)
+  // Original files (v0) should only be leaves if they have no processed versions at all
+  const leafFiles = StirlingFileStubs.filter(stub => {
+    const isParentOfOthers = StirlingFileStubs.some(otherStub => otherStub.parentFileId === stub.id);
+    const isOriginalOfOthers = StirlingFileStubs.some(otherStub => otherStub.originalFileId === stub.id);
+
+    // A file is a leaf if:
+    // 1. It's not a parent of any other files, AND
+    // 2. It has processing history (versionNumber > 0) OR it's not referenced as original by others
+    return !isParentOfOthers && (stub.versionNumber && stub.versionNumber > 0 || !isOriginalOfOthers);
+  });
+
+  // For each leaf file, build its complete lineage path back to original
+  for (const leafFile of leafFiles) {
+    const lineagePath: StirlingFileStub[] = [];
+    let currentFile: StirlingFileStub | undefined = leafFile;
+
+    // Trace back through parentFileId chain to build this specific branch
+    while (currentFile) {
+      lineagePath.push(currentFile);
+
+      // Move to parent file in this branch
+      let nextFile: StirlingFileStub | undefined = undefined;
+
+      if (currentFile.parentFileId) {
+        nextFile = fileMap.get(currentFile.parentFileId);
+      } else if (currentFile.originalFileId && currentFile.originalFileId !== currentFile.id) {
+        // For v1 files, the original file might be referenced by originalFileId
+        nextFile = fileMap.get(currentFile.originalFileId);
+      }
+
+      // Check for infinite loops before moving to next
+      if (nextFile && lineagePath.some(file => file.id === nextFile!.id)) {
+        break;
+      }
+
+      currentFile = nextFile;
+    }
+
+    // Sort lineage with latest version first (leaf at top)
+    lineagePath.sort((a, b) => (b.versionNumber || 0) - (a.versionNumber || 0));
+
+    // Use leaf file ID as the group key - each branch gets its own group
+    groups.set(leafFile.id, lineagePath);
+  }
+
+  return groups;
+}
+
+/**
+ * Check if a file has version history
+ */
+export function hasVersionHistory(fileStub: StirlingFileStub): boolean {
+  return !!(fileStub.originalFileId && fileStub.versionNumber && fileStub.versionNumber > 0);
+}
+
+