fix(#104): enforce storage quota on uploads & fix usage tracking

Backend:
- Add QuotaExceeded error kind mapped to HTTP 507 Insufficient Storage
- Add check_storage_quota() and get_user_storage_info() to StorageUsagePort
- Enforce quota in upload_file_with_cache, upload_file_with_thumbnails (AuthUser extractor)
- Enforce quota in chunked upload create_upload handler
- Add update_user_storage_usage_by_username() for username-based lookup
- Fix extract_username_from_path() to handle subfolders (take first segment only)
- Fix maybe_update_storage_usage() to use username-based lookup instead of passing
  username to get_user_by_id (which always failed silently)

Frontend:
- Parse and display quota error messages on upload failure (507 / QuotaExceeded)
- Stop remaining uploads when quota is exceeded
- Call refreshUserData() after uploads to update storage usage display
- Bump service worker cache to v9

static/js/fileOperations.js

@@ -128,7 +128,15 @@ const fileOps = {
                         fileRowElements.icon.innerHTML = '<i class="fas fa-exclamation-circle"></i>';
                         fileRowElements.icon.classList.add('error');
                     }
-                    resolve({ ok: false });
+                    // Parse error body for quota-exceeded or other messages
+                    let errorMsg = null;
+                    let isQuotaError = false;
+                    try {
+                        const errBody = JSON.parse(xhr.responseText);
+                        errorMsg = errBody.error || null;
+                        isQuotaError = errBody.error_type === 'QuotaExceeded' || xhr.status === 507;
+                    } catch (_) {}
+                    resolve({ ok: false, errorMsg, isQuotaError });
                 }
             });
 
@@ -208,7 +216,14 @@ const fileOps = {
                 console.log(`Successfully uploaded ${file.name}`, result.data);
             } else {
                 console.error(`Upload error for ${file.name}`);
-                window.ui.showNotification('Error', `Error uploading file: ${file.name}`);
+                if (result.isQuotaError) {
+                    const msg = result.errorMsg || window.i18n?.t('storage_quota_exceeded') || 'Storage quota exceeded';
+                    window.ui.showNotification('Error', `${file.name}: ${msg}`);
+                    // Stop uploading remaining files — quota is full
+                    break;
+                } else {
+                    window.ui.showNotification('Error', `Error uploading file: ${file.name}`);
+                }
             }
         }
 
@@ -218,6 +233,11 @@ const fileOps = {
         // Wait for backend to persist, then reload
         await new Promise(resolve => setTimeout(resolve, 800));
 
+        // Refresh storage usage display
+        if (typeof window.refreshUserData === 'function') {
+            try { await window.refreshUserData(); } catch (_) {}
+        }
+
         try {
             await window.loadFiles({ forceRefresh: true });
         } catch (reloadError) {
@@ -330,6 +350,11 @@ const fileOps = {
                 console.log(`Uploaded: ${file.webkitRelativePath}`);
             } else {
                 console.error(`Error uploading ${file.webkitRelativePath}`);
+                if (result.isQuotaError) {
+                    const msg = result.errorMsg || window.i18n?.t('storage_quota_exceeded') || 'Storage quota exceeded';
+                    window.ui.showNotification('Error', `${file.name}: ${msg}`);
+                    break;
+                }
             }
         }
         
@@ -337,6 +362,11 @@ const fileOps = {
         this._finishUploadToast(successCount, totalFiles);
         
         await new Promise(resolve => setTimeout(resolve, 800));
+
+        // Refresh storage usage display
+        if (typeof window.refreshUserData === 'function') {
+            try { await window.refreshUserData(); } catch (_) {}
+        }
         
         try {
             await window.loadFiles({ forceRefresh: true });