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>

clients/apple/Tests/PunktfunkKitTests/SharedFoundationTests.swift

@@ -18,7 +18,7 @@ final class SharedFoundationTests: XCTestCase {
             name: "Tower", address: "192.168.1.173", port: 9777,
             pinnedSHA256: Data([0xDE, 0xAD, 0xBE, 0xEF]),
             lastConnected: Date(timeIntervalSince1970: 1_700_000_000),
-            mgmtPort: 47990, macAddresses: ["aa:bb:cc:dd:ee:ff"])
+            mgmtPort: 47990, macAddresses: ["aa:bb:cc:dd:ee:ff"], clipboardSync: true)
 
         let data = try JSONEncoder().encode(host)
         let decoded = try JSONDecoder().decode(StoredHost.self, from: data)
@@ -39,6 +39,7 @@ final class SharedFoundationTests: XCTestCase {
         XCTAssertNil(decoded.macAddresses)
         XCTAssertNil(decoded.pinnedSHA256)
         XCTAssertNil(decoded.lastConnected)
+        XCTAssertNil(decoded.clipboardSync)
         // Resolvers fall back cleanly.
         XCTAssertEqual(decoded.effectiveMgmtPort, punktfunkDefaultMgmtPort)
         XCTAssertEqual(decoded.wakeMacs, [])