merge(core): reconcile the W7/W8 client refactor with origin's shared-clipboard feature

origin/main landed the shared clipboard (design/clipboard-and-file-transfer.md) while
this branch split quic/msgs.rs -> quic/{caps,control,...} and client.rs ->
client/{mod,control,worker,pump,planes,...} (W7) and deleted the two monoliths. The
feature had modified both deleted files, so its delta is re-applied onto the split
instead of resurrecting the monoliths:

  - HOST_CAP_CLIPBOARD                         -> quic/caps.rs
  - MSG_CLIP_* / CLIP_* consts, the six Clip*
    structs, and their encode/decode impls     -> quic/control.rs (beside the clock codecs)
  - CtrlRequest::{ClipControl,ClipOffer} +
    Negotiated.host_caps                        -> client/control.rs
  - WorkerArgs.{clip_event_tx,clip_cmd_rx}      -> client/worker.rs
  - CLIP_EVENT_QUEUE                            -> client/planes.rs
  - NativeClient clip fields, the 7 clip_* /
    host_caps / next_clip methods, connect()
    channel wiring                              -> client/mod.rs
  - the control-task encode/decode arms and
    the clipboard-task spawn                     -> client/pump.rs

Cargo.lock reconciled (adds pf-clipboard), punktfunk-host/Cargo.toml unions the W6
pf-* subsystem deps with pf-clipboard, and include/punktfunk_core.h is the cbindgen
union (clipboard + rumble C-ABI). punktfunk-core builds --all-features and its 174
lib tests pass, including quic::tests::clip_loopback.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-core/src/client/worker.rs

@@ -1,6 +1,7 @@
 //! `WorkerArgs` (the pump's constructor payload) and `reject_from_close`.
 
 use super::*;
+use crate::clipboard::{ClipCommand, ClipEventCore};
 use crate::config::{CompositorPref, GamepadPref, Mode};
 use crate::error::Result;
 use crate::input::InputEvent;
@@ -38,6 +39,11 @@ pub(crate) struct WorkerArgs {
     pub(crate) rich_input_rx: tokio::sync::mpsc::UnboundedReceiver<RichInput>,
     pub(crate) ctrl_rx: tokio::sync::mpsc::Receiver<CtrlRequest>,
     pub(crate) ctrl_tx: tokio::sync::mpsc::Sender<CtrlRequest>,
+    /// Inbound clipboard event plane feed — the control task pushes ClipState/ClipOffer, the
+    /// clipboard task pushes fetch data; drained by [`NativeClient::next_clip`].
+    pub(crate) clip_event_tx: SyncSender<ClipEventCore>,
+    /// Outbound clipboard fetch/serve/cancel commands from the embedder → [`crate::clipboard::run`].
+    pub(crate) clip_cmd_rx: tokio::sync::mpsc::UnboundedReceiver<ClipCommand>,
     pub(crate) ready_tx: std::sync::mpsc::Sender<Result<Negotiated>>,
     pub(crate) shutdown: Arc<AtomicBool>,
     /// Deliberate-quit flag (see [`NativeClient::quit`]): the worker closes with the quit code if set.