Implement server-side file caching with service principal auth

- Remove progress meter for faster perceived load times
- Fix async getGraphToken() calls with await
- Implement service principal (app-only) authentication for file caching
- Pre-cache jobs (2242 jobs) at startup via Redis
- Background file caching for first 300 jobs on continuous cycle
- Cache refreshes every 5 minutes to keep data current
- All caches served instantly from Redis for all users/devices
- No user authentication required for backend caching
- App token auto-refreshes every 55 minutes

Changes:
- backend/src/index.ts: Added service principal flow, startup cache warming, background file caching
- frontend/public/index.html: Removed progress bar, fixed getGraphToken() awaits
- .env.example: Added GRAPH_TOKEN documentation

frontend/public/index.html

@@ -60,10 +60,6 @@
   </div>
   <h1 class="m-0 mb-3 text-center text-blue-600 text-[33px] font-bold">Job Info</h1>
 
-  <div class="w-full bg-blue-50 h-1.5 rounded overflow-hidden mb-3">
-    <div id="progressBar" class="h-full w-0 bg-blue-600 transition-all duration-300 ease-out"></div>
-  </div>
-
   <div class="relative mb-2">
     <input id="searchBox" placeholder="Search jobs (just start typing or use voice)" class="w-full p-2.5 pr-12 rounded-lg border border-gray-300 text-lg placeholder:text-gray-400">
     <button id="voiceSearchBtn" class="absolute right-2 top-1/2 -translate-y-1/2 w-8 h-8 rounded-full flex items-center justify-center hover:bg-gray-100 transition-colors" title="Voice search">
@@ -289,7 +285,6 @@
   }
   window.clearJobsCache = clearJobsCache;
 
-  const progressBar = document.getElementById('progressBar');
   const searchBox = document.getElementById('searchBox');
   const resultsEl = document.getElementById('results');
   const filtersPanel = document.getElementById('filtersPanel');
@@ -341,19 +336,8 @@
   }
   loadVersion();
 
-  let progTimer=null;
-  function startProgress(){
-    if(progTimer) clearInterval(progTimer);
-    let simulatedProg=0;
-    progTimer=setInterval(()=>{
-      if(simulatedProg<65){ simulatedProg+=0.8; progressBar.style.width=Math.min(65,simulatedProg).toFixed(1)+'%'; }
-    },150);
-  }
-  function finishProgress(){ if(progTimer) clearInterval(progTimer); progressBar.style.width='100%'; setTimeout(()=>{progressBar.parentElement.classList.add('hidden');},400); }
-
   // --- Fetch all jobs ---
   async function fetchAllJobs(){
-    startProgress();
     clearJobsCache('Loading…');
     const startTime = performance.now();
     let pollCount = 0;
@@ -367,20 +351,17 @@
         if (pollCount === 0 || jobsCache.length === 0) {
           jobsCache.length = 0;
           jobsCache.push(...items);
-          progressBar.style.width='95%';
           applyFiltersAndRender();
         }
         if (data.partial) {
           // If partial, poll again after short delay
           pollCount++;
           if (pollCount < 10) setTimeout(pollJobs, 600);
-          else finishProgress();
         } else {
-          finishProgress();
           const loadTime = Math.round(performance.now() - startTime);
           console.log(`✓ Loaded ${items.length} jobs from API in ${loadTime}ms`);
         }
-      }catch(err){ finishProgress(); alert('Failed to fetch jobs: '+err.message); console.error(err); }
+      }catch(err){ alert('Failed to fetch jobs: '+err.message); console.error(err); }
     }
     pollJobs();
   }
@@ -1567,7 +1548,7 @@
   async function loadFilesForNotes(folderLink) {
     console.log('loadFilesForNotes called with:', folderLink);
     
-    const graphToken = getGraphToken();
+    const graphToken = await getGraphToken();
     const headers = graphToken ? { 'x-graph-token': graphToken } : {};
     
     try {
@@ -2222,15 +2203,18 @@
     return 'other';
   };
 
-  // File cache for preloading
+  // File cache for client-side only (server handles pre-caching)
   const fileCache = new Map();
 
   async function preloadJobFiles(job) {
     const link = job.Job_Folder_Link;
-    if (!link || fileCache.has(link)) return; // Skip if no link or already cached
-
+    if (!link) return;
+    
+    // Simple client-side cache check
+    if (fileCache.has(link)) return;
+    
     try {
-      const graphToken = getGraphToken();
+      const graphToken = await getGraphToken();
       const headers = graphToken ? { 'x-graph-token': graphToken } : {};
 
       const controller = new AbortController();
@@ -2246,11 +2230,14 @@
           ...f,
           driveId: f.driveId || rootDriveId
         }));
-        fileCache.set(link, { items, driveId: rootDriveId });
-        console.log(`Preloaded ${items.length} files for job ${job.Job_Number}`);
+        fileCache.set(link, { items, driveId: rootDriveId, cachedAt: Date.now() });
+        console.log(`✓ Cached ${items.length} files for job ${job.Job_Number}`);
       }
     } catch (err) {
-      console.log('Preload failed (non-critical):', err);
+      // Silently fail for background caching
+      if (err.name !== 'AbortError') {
+        console.debug(`Cache skip for job ${job.Job_Number}:`, err.message);
+      }
     }
   }
 
@@ -2515,7 +2502,7 @@
       return;
     }
 
-    const graphToken = getGraphToken();
+    const graphToken = await getGraphToken();
     if (!graphToken) {
       console.warn('Graph token missing; using fallback URL');
       openFileInViewer(fallbackUrl, name);
@@ -2755,7 +2742,7 @@
       </div>
     `;
 
-    const graphToken = getGraphToken();
+    const graphToken = await getGraphToken();
     const headers = graphToken ? { 'x-graph-token': graphToken } : {};
 
     try {