refactor(mobile): extract shared MIME type utility and improve error handling

- Extract EXT_TO_MIME map and mimeTypeFromFilename to shared module
  at mobile/src/utils/mimeTypes.ts (used by _layout.tsx and +not-found.tsx)
- Add error logging to ensureLocalUri catch block for debugging
- Add error handling to Linking.openURL calls in ProfileScreen
- Fix incorrect LSSupportsOpeningDocumentsInPlace docs in audit report

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

mobile/app/_layout.tsx

@@ -23,6 +23,7 @@ import { ActivityIndicator, StyleSheet, Text, View } from "react-native";
 import { SafeAreaProvider } from "react-native-safe-area-context";
 import { AuthProvider, useAuth } from "../src/context/AuthContext";
 import { ShareProvider, useShare } from "../src/context/ShareContext";
+import { mimeTypeFromFilename } from "../src/utils/mimeTypes";
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -50,44 +51,6 @@ function filenameFromUri(uri: string): string {
   }
 }
 
-/**
- * Common MIME type mappings for file extensions.
- * Used to infer the MIME type of files shared via the Share Sheet / "Open In…"
- * so the server receives a correct Content-Type instead of application/octet-stream.
- */
-const EXT_TO_MIME: Record<string, string> = {
-  pdf: "application/pdf",
-  jpg: "image/jpeg",
-  jpeg: "image/jpeg",
-  png: "image/png",
-  gif: "image/gif",
-  bmp: "image/bmp",
-  tiff: "image/tiff",
-  tif: "image/tiff",
-  webp: "image/webp",
-  heic: "image/heic",
-  heif: "image/heif",
-  txt: "text/plain",
-  csv: "text/csv",
-  doc: "application/msword",
-  docx: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
-  xls: "application/vnd.ms-excel",
-  xlsx: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
-  ppt: "application/vnd.ms-powerpoint",
-  pptx: "application/vnd.openxmlformats-officedocument.presentationml.presentation",
-  rtf: "application/rtf",
-  html: "text/html",
-  xml: "application/xml",
-  json: "application/json",
-  zip: "application/zip",
-};
-
-/** Infer MIME type from a filename's extension, or undefined if unknown. */
-function mimeTypeFromFilename(filename: string): string | undefined {
-  const ext = filename.split(".").pop()?.toLowerCase();
-  return ext ? EXT_TO_MIME[ext] : undefined;
-}
-
 /**
  * Build a Linking URL handler that forwards incoming file:// / content://
  * URLs to ShareContext.  Extracted as a module-level factory so the handler