feat(privacy): strip EXIF/XMP/IPTC from image uploads by default (#109)

Metadata was only dropped as a side effect of opt-in compression, so a
phone photo carried its GPS fix, camera model and timestamp into the room
and the media store. utils/stripImageMetadata.ts now removes it at the
container level, without touching pixels: JPEG drops APP1/APP13/COM
(writing back a minimal EXIF holding only Orientation when it isn't 1,
so sideways-stored photos still display upright), PNG drops eXIf and the
text chunks XMP lives in, WebP drops EXIF/XMP and clears the VP8X flags.
Other types pass through.

Applied before encryption on every composer path (attach, paste, drop,
share target) and to user/room avatar picks; GIF upload is excluded.
Setting → General → Privacy "Remove Photo Metadata Before Sending",
default on. The upload card says "Photo metadata removed".

Unit tests on generated fixtures with a GPS IFD (JPEG orientation 6,
JPEG + comment, PNG with eXIf + XMP, WebP with EXIF); verified end to
end: the bytes stored by Synapse decode fine and carry only Orientation.

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

src/app/features/common-settings/general/RoomProfile.tsx

@@ -43,7 +43,10 @@ import { sendStateEvent } from '../../../utils/room';
 import { CompactUploadCardRenderer } from '../../../components/upload-card';
 import { useObjectURL } from '../../../hooks/useObjectURL';
 import { createUploadAtom, UploadSuccess } from '../../../state/upload';
+import { stripImageMetadata as stripImageMetadata_ } from '../../../utils/stripImageMetadata';
 import { useFilePicker } from '../../../hooks/useFilePicker';
+import { useSetting } from '../../../state/hooks/settings';
+import { settingsAtom } from '../../../state/settings';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
 import { useAlive } from '../../../hooks/useAlive';
 import { RoomPermissionsAPI } from '../../../hooks/useRoomPermissions';
@@ -138,7 +141,19 @@ export function RoomProfileEdit({
     return undefined;
   }, [imageFile]);
 
-  const pickFile = useFilePicker(setImageFile, false);
+  // [Gitea #109] Avatars go through the same metadata strip as messages.
+  const [stripImageMetadata] = useSetting(settingsAtom, 'stripImageMetadata');
+  const pickFile = useFilePicker(
+    useCallback(
+      (file: File) => {
+        (stripImageMetadata ? stripImageMetadata_(file) : Promise.resolve({ file })).then((r) =>
+          setImageFile(r.file),
+        );
+      },
+      [stripImageMetadata],
+    ),
+    false,
+  );
 
   const handleRemoveUpload = useCallback(() => {
     setImageFile(undefined);