feat(session): Skia console UI — overlay contract + stats OSD/capture HUD (phase 4a)

The §6.1 presenter↔console-UI contract lands: pf-presenter exposes its
device (SharedDevice) and composites at most one premultiplied-alpha
quad per frame (new overlay.frag + LOAD render pass over the swapchain;
zero cost while the overlay returns None). pf-console-ui implements it
with skia-safe on the shared VkDevice: DirectContext via the ash
dispatch chain, a ring of two offscreen render targets (one-frame-in-
flight safe), damage-driven redraws — the OSD re-renders at 1 Hz, the
hint on capture toggles, nothing per-frame. Skia never touches the
swapchain. The session binary carries it behind the default ui feature:
4.9 MB stripped without, 10 MB with (measured).

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

crates/pf-console-ui/src/lib.rs

@@ -0,0 +1,15 @@
+//! The Skia console UI (punktfunk-planning `linux-client-rearchitecture.md` §6): an
+//! [`Overlay`] implementation rendering on the PRESENTER's Vulkan device into offscreen
+//! RGBA images the presenter composites as one premultiplied quad. Skia never touches
+//! the swapchain, and nothing here runs while the overlay has nothing to show — the
+//! §6.1 invariants live or die in this crate.
+//!
+//! Milestone 1 (this file): the stats OSD panel + the capture-hint pill — small on
+//! purpose, it proves the whole shared-device pipeline. The gamepad library moves in
+//! next.
+
+#[cfg(target_os = "linux")]
+mod skia_overlay;
+
+#[cfg(target_os = "linux")]
+pub use skia_overlay::SkiaOverlay;