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-client-core/src/trust.rs

@@ -544,6 +544,16 @@ pub struct Settings {
     /// "Invert scroll direction"). Default off = the host scrolls the way this machine does.
     #[serde(default)]
     pub invert_scroll: bool,
+    /// Playback endpoint for stream audio — on Linux the PipeWire `node.name` the
+    /// playback stream targets (`target.object`); empty = the session default (the
+    /// Apple client's Speaker picker). The session maps it onto `PUNKTFUNK_AUDIO_SINK`.
+    /// Ignored on Windows until the WASAPI endpoint leg exists.
+    #[serde(default)]
+    pub speaker_device: String,
+    /// Capture endpoint for the mic uplink (same semantics as `speaker_device`;
+    /// `PUNKTFUNK_AUDIO_SOURCE`).
+    #[serde(default)]
+    pub mic_device: String,
     /// Match-window resolution policy (design/midstream-resolution-resize.md D1): the
     /// stream mode follows the session window — the connect asks for the window's pixel
     /// size and a mid-session resize renegotiates the host's virtual display + encoder
@@ -634,6 +644,8 @@ impl Default for Settings {
             library_enabled: false,
             auto_wake: true,
             invert_scroll: false,
+            speaker_device: String::new(),
+            mic_device: String::new(),
             match_window: false,
             last_window_w: 0,
             last_window_h: 0,