feat(client): device-pick plumbing — GPU enumeration + audio endpoint targeting

The Settings GPU pick existed (adapter → PUNKTFUNK_VK_ADAPTER) but no Linux
shell could enumerate anything to pick: the GTK shell deliberately links no
Vulkan. pf_presenter::vk::list_adapters() reads the physical devices'
marketing names (no surface, discrete first, deduped — the name is the whole
match key in pick_device), surfaced as `punktfunk-session --list-adapters`.

Audio gets the same treatment for the new speaker_device/mic_device settings
(PipeWire node.name; empty = default): session main maps them onto
PUNKTFUNK_AUDIO_SINK/SOURCE — a hand-set env still wins, like the adapter —
and the playback/mic streams pass them as `target.object` (raw key: the
keys::TARGET_OBJECT constant is feature-gated on a newer libpipewire than we
require). pf_client_core::audio::devices() is the registry roundtrip the
pickers read, exposed for debugging as `punktfunk-session --list-audio`.
The WASAPI leg (Windows endpoint IDs) is still to come; the fields are
ignored there.

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

crates/pf-presenter/src/vk/mod.rs

@@ -33,6 +33,8 @@ mod reconfig;
 mod resources;
 mod setup;
 
+pub use setup::list_adapters;
+
 /// One presenter iteration's video input.
 pub enum FrameInput<'a> {
     /// No new frame — re-composite the retained video image (expose/resize).