feat(clipboard): Linux + Windows host clipboard backends (Phase 1 host + Phase 3)

Host-side real-session-clipboard integration, reached through the portable
ClipCoordCmd seam so punktfunk1.rs stays platform-agnostic (design
clipboard-and-file-transfer.md §4). Advertised + started only when the operator
policy (PUNKTFUNK_CLIPBOARD, default off) allows it and the session mirrors a
live compositor.

clipboard/ module (gated cfg(any(linux, windows))):
- mod.rs — the unified HostClipboard enum + §3.5 wire<->platform normalization
  and the shared ClipEvent / PasteResponder.
- wayland.rs — ext-data-control-v1 (KWin / wlroots / Sway / Hyprland), the
  preferred Linux backend. On-glass verified on Hyprland.
- mutter.rs — GNOME. Mutter ships no wl/ext data-control at any version, so this
  talks to its DIRECT org.gnome.Mutter.RemoteDesktop clipboard (the xdg portal
  needs an interactive grant a headless host can't answer). On-glass on GNOME.
- windows.rs — the Win32 clipboard on a dedicated message-loop window:
  AddClipboardFormatListener -> WM_CLIPBOARDUPDATE for host copies, OLE delayed
  rendering (WM_RENDERFORMAT) for host pastes, per-window state via GWLP_USERDATA.
- winfmt.rs — pure Win32<->wire byte conversions (CF_HTML offset math, UTF-16
  text, RTF NUL trim), unit-tested on any host (cfg(any(windows, test))).
- session.rs — the backend-agnostic per-session coordinator owning all four data
  paths (host copy->client, client fetch, client copy->host, host paste).

Cargo.toml: windows crate gains Win32_System_DataExchange + Win32_System_Ole.

Verified: Linux builds + clippy + 282 host tests + fmt clean; the full host crate
compiles native on x86_64-pc-windows-msvc (checked on the RTX box).

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

crates/punktfunk-host/Cargo.toml

@@ -88,9 +88,11 @@ openh264 = "0.9"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 # `screencast` gates the ScreenCast portal module; `remote_desktop` adds the RemoteDesktop
-# portal we use for libei input on KWin/GNOME; `tokio` is the default runtime.
-# `open_pipe_wire_remote` is unconditional, so ashpd's own `pipewire` feature is not
-# needed — we drive PipeWire with the `pipewire` crate below.
+# portal we use for libei input on KWin/GNOME; `tokio` is the default runtime. `open_pipe_wire_remote`
+# is unconditional, so ashpd's own `pipewire` feature is not needed — we drive PipeWire with the
+# `pipewire` crate below. (The GNOME shared-clipboard backend uses Mutter's *direct*
+# `org.gnome.Mutter.RemoteDesktop.Session` clipboard via raw `ashpd::zbus` — NOT the xdg
+# `org.freedesktop.portal.Clipboard`, which needs interactive approval — so no `clipboard` feature.)
 ashpd = { version = "0.13", features = ["screencast", "remote_desktop"] }
 ffmpeg-next = "8"
 libc = "0.2"
@@ -115,7 +117,7 @@ wayland-protocols-wlr = { version = "0.3", features = ["client"] }
 wayland-protocols-misc = { version = "0.3", features = ["client"] }
 # `xdg-output` (zxdg_output_v1): the per-output *logical* geometry (post-scale size + global
 # position), used by the KWin fake_input backend to map absolute coordinates under display scaling.
-wayland-protocols = { version = "0.32", features = ["client"] }
+wayland-protocols = { version = "0.32", features = ["client", "staging"] }
 # Codegen for KDE's `zkde_screencast_unstable_v1` (vendored in `protocols/`): create a KWin
 # virtual output sized to the client's resolution and get its PipeWire node (KRdp's path).
 # `wayland-backend` is referenced by the generated interface tables.
@@ -200,6 +202,11 @@ windows = { version = "0.62", features = [
     # See capture/windows/dxgi.rs `install_gpu_pref_hook`. No trampoline (we fully replace the fn) → no detour
     # crate / no C length-disassembler dep; a 12-byte absolute-jmp prologue patch suffices.
     "Win32_System_Memory",
+    # Shared-clipboard host backend (src/clipboard/windows.rs): the Win32 clipboard API
+    # (Open/Get/SetClipboardData, AddClipboardFormatListener, delayed rendering) plus the
+    # CLIPBOARD_FORMAT / CF_UNICODETEXT newtype from Ole (design/clipboard-and-file-transfer.md §3).
+    "Win32_System_DataExchange",
+    "Win32_System_Ole",
     # Per-monitor-v2 DPI awareness — IDXGIOutput5::DuplicateOutput1 (the modern capture path Apollo
     # uses; FP16/format-list, robust to overlay/format churn) requires the process to be DPI-aware.
     "Win32_UI_HiDpi",