feat(client): Vulkan session binary — SDL3 + ash presenter MVP (phase 1)

punktfunk-session streams one --connect session in an SDL3 window: ash
swapchain with a transfer-only letterboxed blit of the software-decode
path (no graphics pipeline until the phase-2 dmabuf/CSC pass), the
ui_stream input-capture state machine on SDL events (scancode→VK table
cross-checked against the evdev one), gamepads via a new caller-pumped
GamepadService mode (SDL video owns the main thread here), and the
shell↔session stdout contract: {"ready":true}, per-window stats:
lines, JSON error + exit codes 0/2/3/4. Strict trust — no pin, no
connect. Design: punktfunk-planning linux-client-rearchitecture.md.

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

crates/pf-presenter/src/lib.rs

@@ -0,0 +1,21 @@
+//! The Vulkan session presenter (punktfunk-planning `linux-client-rearchitecture.md`,
+//! Phase 1): an SDL3 window + ash swapchain that presents the shared session pump's
+//! decoded frames, captures input on the `ui_stream` state-machine contract, and reports
+//! the unified stats window on stdout. No UI toolkit anywhere in the dependency tree.
+//!
+//! Phase 1 is the software path: `CpuFrame` RGBA uploads + a transfer-only letterbox
+//! blit (no graphics pipeline, no shaders — those arrive with the Phase 2 dmabuf/CSC
+//! pass). A hardware (dmabuf) frame slipping through demotes the decoder to software via
+//! the session pump's `force_software` contract, same as the GTK presenter.
+
+#[cfg(target_os = "linux")]
+pub mod input;
+#[cfg(target_os = "linux")]
+pub mod keymap_sdl;
+#[cfg(target_os = "linux")]
+mod run;
+#[cfg(target_os = "linux")]
+pub mod vk;
+
+#[cfg(target_os = "linux")]
+pub use run::{run_session, Outcome, SessionOpts};