fix(mobile): iOS share sheet, empty files tab, and stuck upload status

- app.json: add CFBundleDocumentTypes to iOS infoPlist so the app
  appears in the iOS Share Sheet; add ACTION_SEND/SEND_MULTIPLE
  intentFilters for Android share intent support

- src/context/ShareContext.tsx (new): React context that queues files
  received from the share sheet and delivers them to UploadScreen

- app/_layout.tsx: wrap in ShareProvider; add Linking handler
  (makeUrlHandler factory + getInitialURL cold-start + addEventListener
  warm-start) to capture file:// and content:// URLs

- src/services/api.ts: fix FileRecord interface (original_filename,
  nested ProcessingStatus, mime_type); fix UploadResponse interface;
  fix listFiles() (per_page param, unwrap data.files); add
  getFileStatus(fileId) for single-file status polling

- src/screens/FilesScreen.tsx: use file.original_filename and
  file.processing_status.status; fix statusEmoji to use actual backend
  status values (completed/pending/duplicate)

- src/screens/UploadScreen.tsx: consume ShareContext for auto-upload of
  shared files; add 5-second polling loop (search by filename → file_id
  → getFileStatus) to show real-time server processing status;
  uploadFile wrapped in useCallback; proper effect dependency arrays

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

mobile/app.json

@@ -21,7 +21,27 @@
         "NSPhotoLibraryUsageDescription": "DocuElevate accesses your photo library to select documents for upload.",
         "NSPhotoLibraryAddUsageDescription": "DocuElevate saves scanned documents to your photo library.",
         "UIBackgroundModes": ["fetch", "remote-notification"],
-        "ITSAppUsesNonExemptEncryption": false
+        "ITSAppUsesNonExemptEncryption": false,
+        "CFBundleDocumentTypes": [
+          {
+            "CFBundleTypeName": "All Documents",
+            "CFBundleTypeRole": "Viewer",
+            "LSHandlerRank": "Alternate",
+            "LSItemContentTypes": [
+              "public.content",
+              "public.data",
+              "public.image",
+              "com.adobe.pdf",
+              "public.plain-text",
+              "org.openxmlformats.wordprocessingml.document",
+              "org.openxmlformats.spreadsheetml.sheet",
+              "org.openxmlformats.presentationml.presentation",
+              "com.microsoft.word.doc",
+              "com.microsoft.excel.xls",
+              "com.microsoft.powerpoint.ppt"
+            ]
+          }
+        ]
       },
       "buildNumber": "3"
     },
@@ -38,6 +58,18 @@
         "RECEIVE_BOOT_COMPLETED",
         "VIBRATE"
       ],
+      "intentFilters": [
+        {
+          "action": "SEND",
+          "data": [{ "mimeType": "*/*" }],
+          "category": ["DEFAULT"]
+        },
+        {
+          "action": "SEND_MULTIPLE",
+          "data": [{ "mimeType": "*/*" }],
+          "category": ["DEFAULT"]
+        }
+      ],
       "versionCode": 1
     },
     "web": {