release: v4.8.11 file transfer reliability fix

fix(file-transfer): size chunks under the 64KB SCTP message limit

Each 64KB chunk became a ~87KB AES-GCM+Base64 file_chunk message,
exceeding WebRTC's 64KB SCTP message-size floor. The consent handshake
(small messages) succeeded, but no chunk was ever delivered on Safari
and cross-browser connections whose SDP omits a=max-message-size, so
files never transferred. Send chunk size is now 16KB (~22KB on the
wire); inbound chunks up to 64KB stay accepted for backward compat.

fix(file-transfer): make MIME advisory, drive validation by extension

The client-supplied MIME type is easily spoofed and varies across
browsers/OSes, yet was a hard gate: files with an empty MIME or a
cross-OS variant (application/x-zip-compressed, image/jpg) were wrongly
rejected. Extension allow-list plus BLOCKED_EXTENSIONS is now the
boundary; a blatantly foreign MIME on a safe extension is still rejected
and per-type size limits still apply.

meta.json

@@ -1,10 +1,10 @@
 {
-  "version": "1781588965220",
-  "buildVersion": "1781588965220",
-  "appVersion": "4.8.10",
-  "buildTime": "2026-06-16T05:49:25.266Z",
-  "buildId": "1781588965220-6dac4ce",
-  "gitHash": "6dac4ce",
+  "version": "1781648539643",
+  "buildVersion": "1781648539643",
+  "appVersion": "4.8.11",
+  "buildTime": "2026-06-16T22:22:19.692Z",
+  "buildId": "1781648539643-9244250",
+  "gitHash": "9244250",
   "generated": true,
-  "generatedAt": "2026-06-16T05:49:25.268Z"
+  "generatedAt": "2026-06-16T22:22:19.693Z"
 }