[foxnne]

Part of fizzyedit/work#40 (EMBEDDED_EDITOR_PLAN step 3, fizzyedit/work#32)

What changes

A remote client (an adapter in Blender, Unreal, …) can now connect to the control socket, GET /remote with Upgrade: fizzy-remote-view/1, and speak the sdk/remote protocol: open a view, send pointer/key/text input, ask for frames and get them. Without the upgrade header the answer is 426, with another method 405. The socket stays 0600 and same-user.

• app/control/Link.zig + Server.zig: an upgraded connection becomes two byte queues. A reader and a writer task per connection do the waiting; the UI thread drains and fills the queues once per frame (Service.pump). No thread per view, and the UI thread never blocks.
• app/remote/RemoteViewHost.zig: a ViewHost that the OS never shows. ViewHost's vtable is unchanged. Input waits in the host as dvui events until inject(win); keys and text only while the client says the view is focused. A view the client closes, or one that goes with a dropped connection, is dropped from its session.
• app/remote/Session.zig / Service.zig: one conversation per client over Endpoint, and the registry. fizzy.remote.views (internal) lists the open views.
• app/remote/encoder.zig: the stub, one quad filling the view.
• app/remote/keys.zig: Key.code is read as a USB HID usage (the numbering SDL scancodes use). This is a decision I made, not one the plan states; please check it.
• docs/CONTROL.md: the route and fizzy.remote.views.

SDK impact

• None

(sdk_version untouched; sdk/remote is only imported by the app module, in build/sdk.zig.)

Verified

Tests in app/remote/tests.zig (fizzy-app-tests), among them a client on the real socket: create a view, send motion/click/key/text, ask a frame, drop the connection with a frame request in flight (the session and its view go, fizzy keeps running), then a second client served as before. One editor-facing body of ViewHost calls runs against a local fake host and the remote one. Input is injected into a dvui.testing window and checked at the view's offset. Server.zig has its own tests for the upgraded byte stream.

• macOS:
• Windows:
• Linux: scripts/check-fmt.sh, build, build test, build test-integration (92/92 steps), build check-web, build test-sdk-version, build lint, build check-tests-reached
• Web: check-web builds; the control server is native only

Follow-ups

• The editor's frame loop does not draw remote views yet (TODO(seam) in Service.zig, EMBEDDED_EDITOR_PLAN step 4). Until it does, input waits in the host (up to 1024 events) and pump answers frame requests itself with the stub. I did not wire the Editor, so remote input cannot land on the main window at the wrong origin.
• The real draw-list encoder replaces encoder.solidFill (TODO(seam)).
• Touch, IME and clipboard messages are accepted and ignored for now.
• The diff is a little over 800 lines outside tests and docs, counting Link/Server upgrade code that has to travel with the route.
• I had no jj in this cloud session (its release download is blocked and the checkout has no .jj), so this branch was committed with git.

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