feat(host,web): multi-GPU selection — GPU inventory + preference API, web-console GPU card

- new crate::gpu (compiled on all platforms so the OpenAPI doc stays
  platform-independent): DXGI / sysfs GPU inventory with reboot-stable ids
  (PCI vendor:device + occurrence — LUIDs are per-boot), persisted auto/manual
  preference (<config>/gpu-settings.json, atomic temp+rename with in-memory
  rollback), one selection with precedence console preference >
  PUNKTFUNK_RENDER_ADAPTER > max VRAM and graceful fallback when the preferred
  GPU is absent, plus a live "in use" record (RAII session guard wrapped around
  every encoder open_video returns)
- fix: windows_gpu_vendor derived the encoder backend from DXGI adapter 0
  instead of the selected render adapter — on a hybrid box (e.g. Intel iGPU at
  index 0 + NVIDIA dGPU) the backend could disagree with the GPU the capture
  ring / IddCx render pin sit on. The NVENC 4:4:4 probe now also runs on the
  selected adapter (was: OS default), the codec/4:4:4 probe caches are keyed
  per selected GPU (were process-lifetime OnceLocks), and an explicit
  PUNKTFUNK_ENCODER conflicting with the selected GPU's vendor warns up front
- mgmt API: GET /api/v1/gpus (inventory + mode + preferred + next-session
  selection with reason + in-use GPU/backend/session-count) and
  PUT /api/v1/gpus/preference (validates mode/gpu_id before writing);
  openapi.json regenerated; the vdisplay render pin now also engages for a
  console preference (not just the env pin)
- web console: GPU card on the Host page — list with vendor + VRAM,
  Automatic / Prefer controls, Preferred / Next session / "In use · backend"
  badges, missing-preferred-GPU warning and env-pin note; en + de messages
- Linux: a matched manual preference picks the VAAPI render node and the
  NVENC-vs-VAAPI auto choice; auto mode is exactly the previous behavior

Validated live on the hybrid laptop (RTX 3500 Ada + Intel Arc Pro, which
enumerates twice — the occurrence ids disambiguate): enumerate, prefer,
bad-id 400, restart persistence, auto-restore keeping the stored pick.

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

web/messages/en.json

@@ -37,6 +37,16 @@
 	"compositor_available": "Available",
 	"compositor_unavailable": "Unavailable",
 	"compositor_default": "Default",
+	"host_gpus": "GPUs",
+	"host_gpus_help": "The GPU the host captures and encodes on. Automatic picks the best GPU; preferring one pins capture + encode to it. A change applies to the next session.",
+	"gpu_automatic": "Automatic",
+	"gpu_prefer": "Prefer",
+	"gpu_preferred": "Preferred",
+	"gpu_in_use": "In use · {backend}",
+	"gpu_next_session": "Next session",
+	"gpu_none": "No GPUs detected.",
+	"gpu_missing_warning": "The preferred GPU “{name}” is not present — automatic selection is used instead.",
+	"gpu_env_note": "PUNKTFUNK_RENDER_ADAPTER={value} pins the GPU while in automatic mode.",
 	"clients_title": "Paired clients",
 	"clients_empty": "No paired clients yet.",
 	"clients_name": "Name",