feat(pwa): register as an Android share target (#155)

public/manifest.json declares share_target (POST multipart to
/share-target: title/text/url + image/video/audio/pdf/text files). The
service worker answers that POST itself: it stashes the form in a Cache
API bucket and 303s to the in-app /share page, which lists what arrived,
offers a room search, and on pick writes the files into that room's
upload-board atom (encrypting first for E2EE rooms via the composer's
shared filesToUploadItems) and the title/text/url into its draft, then
opens the room — the user still presses Send. The stash is cleared once
placed; reopening /share afterwards says so.

nginx/caddy examples and the prod image config gain a 303 for
/share-target so a POST that reaches the origin before the worker
controls the page lands on /share instead of a 405. iOS has no share
target support and ignores the manifest entry.

Verified headless against the built preview: SW-controlled page → POST
/share-target (two PNGs + title + text) → /share lists both files and the
text → pick the DM → composer shows both files on the upload board and
the text in the draft → /share reports nothing pending.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/RoomInput.tsx

@@ -95,7 +95,7 @@ import {
   createUploadFamilyObserverAtom,
 } from '../../state/upload';
 import { getImageUrlBlob, loadImageElement } from '../../utils/dom';
-import { safeFile } from '../../utils/mimeTypes';
+import { filesToUploadItems } from '../../utils/uploadItems';
 import { fulfilledPromiseSettledResult } from '../../utils/common';
 import { useSetting } from '../../state/hooks/settings';
 import { useAlive } from '../../hooks/useAlive';
@@ -375,36 +375,9 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
     const handleFiles = useCallback(
       async (files: File[]) => {
         setUploadBoard(true);
-        const safeFiles = files.map(safeFile);
-        const fileItems: TUploadItem[] = [];
-
-        if (room.hasEncryptionStateEvent()) {
-          const encryptFiles = fulfilledPromiseSettledResult(
-            await Promise.allSettled(safeFiles.map((f) => encryptFile(f))),
-          );
-          encryptFiles.forEach((ef) =>
-            fileItems.push({
-              ...ef,
-              metadata: {
-                markedAsSpoiler: false,
-              },
-            }),
-          );
-        } else {
-          safeFiles.forEach((f) =>
-            fileItems.push({
-              file: f,
-              originalFile: f,
-              encInfo: undefined,
-              metadata: {
-                markedAsSpoiler: false,
-              },
-            }),
-          );
-        }
         setSelectedFiles({
           type: 'PUT',
-          item: fileItems,
+          item: await filesToUploadItems(room, files),
         });
       },
       [setSelectedFiles, room],