Replace base64-in-JSON file transfers with binary WebSocket frames to
unblock the JS thread when assistant markdown messages contain images.
Receive cost (JSON.parse over multi-MB base64) and persist cost (base64
re-encode to disk) both removed.
- Split daemon-client `exploreFileSystem` into `listDirectory` + `readFile`;
`readFile` returns `{ bytes, mime, size, modifiedAt }`. Encoding stays
private to the seam.
- New `packages/server/src/shared/binary-frames/` module hosts terminal
frames (moved from `terminal-stream-protocol.ts`) and new file-transfer
opcodes (`FileBegin` / `FileChunk` / `FileEnd`) with request-id correlation.
- Add optional `acceptBinary` to `FileExplorerRequestSchema`. New daemons
emit binary frames when set; legacy JSON path remains for old clients.
Compat fallback lives only inside `readFile`.
- New `persistAttachmentFromBytes` writes bytes directly: native via
`expo-file-system` `File.write(Uint8Array)`, web via Blob -> IndexedDB,
desktop via new `write_attachment_bytes` IPC. `persistAttachmentFromBase64`
removed.
