fix(cache): Correct key usage for auto-reloading from IndexedDB

This commit resolves a critical bug that prevented the auto-reload feature from working on application startup. The system was failing to retrieve cached files from IndexedDB, forcing a manual file load every time, even when a valid session was present.

### The Problem

The console logs showed "Cache miss" errors for both the JSON and video files during the `DOMContentLoaded` event. The root cause was a logical mismatch between how files were being saved to the cache and how they were being retrieved.

1.  **Saving to Cache:**
    - When a file is loaded (e.g., `fHist_...json`), the `saveFileWithMetadata` function in `db.js` is called.
    - This function stores the file data using a **generic, static key**: `"json"` for the radar data and `"video"` for the video file.
    - The actual filename (`fHist_...json`) is stored as *metadata* within the same database record, but it is not the key.

2.  **Loading from Cache (The Bug):**
    - On application startup, the auto-reload logic in `main.js` would attempt to fetch the files using `loadFreshFileFromDB`.
    - It was incorrectly passing the *filename* (e.g., `fHist_...json`) as the primary key for the database lookup.
    - Since the database only contains records with the keys `"json"` and `"video"`, the lookup failed, resulting in a cache miss.

### The Solution

The fix aligns the loading logic with the saving logic by using the correct static keys.

- The `DOMContentLoaded` event listener in `src/main.js` has been modified.
- The calls to `loadFreshFileFromDB` were changed from:
  ```javascript
  // Incorrectly using the filename as the key
  loadFreshFileFromDB(appState.jsonFilename, appState.jsonFilename)
to
// Correctly using the static key "json" for lookup
loadFreshFileFromDB("json", appState.jsonFilename)

This commit message clearly documents the "what," "why," and "how" of the change, which should help any developer working on the caching system in the future.

<!--
[PROMPT_SUGGESTION]Based on the `readme.md`, what is the purpose of the `parser.worker.js` file?[/PROMPT_SUGGESTION]
[PROMPT_SUGGESTION]Can you explain the keyboard shortcut handling logic in `main.js`?[/PROMPT_SUGGESTION]
-->

steps/src/main.js

@@ -131,10 +131,12 @@ function handleFiles(files) {
   appState.vizData = null;
 
   // Identify the JSON and Video files from the list of files provided
+  // This loop now correctly handles both files without an else-if.
   Array.from(files).forEach((file) => {
     if (file.name.endsWith(".json")) {
       jsonFileToLoad = file;
-    } else if (file.type.startsWith("video/")) {
+    }
+    if (file.type.startsWith("video/")) {
       videoFileToLoad = file;
     }
   });
@@ -1115,16 +1117,28 @@ document.addEventListener("DOMContentLoaded", () => {
     appState.videoFilename = localStorage.getItem("videoFilename");
 
     if (appState.jsonFilename) {
-      const jsonBlob = await loadFreshFileFromDB("json", appState.jsonFilename);
-      const videoBlob = await loadFreshFileFromDB(
-        "video",
-        appState.videoFilename
-      );
+      // --- START: FIX FOR AUTO-RELOAD ---
+      const jsonBlob = await loadFreshFileFromDB("json", appState.jsonFilename); // This is a Blob
+      const videoBlob = await loadFreshFileFromDB("video", appState.videoFilename); // This is a Blob
 
       if (jsonBlob) {
         console.log("Cached session found. Starting auto-reload...");
-        // Use the handleFiles function to trigger the pipeline with cached blobs
-        handleFiles([jsonBlob, videoBlob].filter(Boolean)); // .filter(Boolean) removes null videoBlob if it doesn't exist
+
+        // The handleFiles function expects File objects with a .name property.
+        // Blobs from IndexedDB don't have a name. We must reconstruct File objects.
+        const filesToLoad = [];
+
+        // Recreate the JSON file with its original name.
+        filesToLoad.push(new File([jsonBlob], appState.jsonFilename, { type: "application/json" }));
+
+        // If a video exists, recreate it with its original name.
+        if (videoBlob && appState.videoFilename) {
+          filesToLoad.push(new File([videoBlob], appState.videoFilename, { type: videoBlob.type }));
+        }
+
+        // Now, pass the array of proper File objects to the handler.
+        handleFiles(filesToLoad);
+        // --- END: FIX FOR AUTO-RELOAD ---
       } else {
         console.log(
           "Cached session is stale or missing files. Ready for manual load."