feat(client): shared clipboard on Windows

The protocol half has been in punktfunk-core since the clipboard work
landed -- the per-session fetch task, plus clip_control/clip_offer/
clip_fetch/clip_serve/next_clip on NativeClient -- but only the Apple
client ever drove it, through the C ABI. The Windows and Linux clients link
the core directly and simply never wired it, so copy-paste between host and
client worked on a Mac and nowhere else.

This adds the missing half: the OS-clipboard bridge, on its own session
thread beside the audio one.

Local -> remote stays lazy by construction, as the design asks: a
GetClipboardSequenceNumber poll spots a local copy and we announce only the
FORMAT LIST; bytes are read when (and only when) the host actually pastes
and sends a FetchRequest.

Remote -> local is EAGER in this first cut, which is a deliberate deviation
worth naming. macOS gets laziness free from NSPasteboardItemDataProvider;
the Windows equivalent is delayed rendering, which needs a clipboard-owning
window running its own message pump. So we fetch on the offer and place real
bytes under a 4 MB cap -- text always crosses, a large image is skipped
rather than pulled for a paste that may never come. Delayed rendering lifts
the cap later.

Echo suppression is the design's Windows rule verbatim (capture the
sequence number right after our own SetClipboardData); without it every
copy ping-pongs between the machines forever. Content marked
ExcludeClipboardContentFromMonitorProcessing -- what password managers set
-- is never announced and never served.

Text and PNG for now. Apps that publish only CF_DIB need the conversion the
host already has. Linux keeps a stub: the bridge itself is
platform-neutral and will drive a data-control seam unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-client-core/src/lib.rs

@@ -41,6 +41,11 @@ mod video_software;
 mod video_vaapi;
 #[cfg(any(target_os = "linux", windows))]
 mod video_vulkan;
+// The OS-clipboard bridge for the shared clipboard (design/clipboard-and-file-transfer.md §5).
+// Built everywhere the session client is; the platform seam inside is Windows-real,
+// stub elsewhere.
+#[cfg(any(target_os = "linux", windows))]
+pub mod clipboard;
 // PyroWave decode — Linux + Windows (plan §4.5; the Apple Metal port is its own phase).
 // Windows joined once its client moved to the SAME spawned Vulkan session presenter as
 // Linux's: the decoder is plain Vulkan compute on the presenter's device (no fds, no