fix(host/windows): NVENC capture on real GPU + HOME-less config dir

Validated live on an RTX 4090 (Windows 11) host streaming to the Rust
reference client over the LAN: SudoVDA virtual display → DXGI Desktop
Duplication (D3D11 zero-copy) → NVENC HEVC → punktfunk/1. 720p60 and
1080p60 both clean (181 / 177 frames, 0 mismatched, p50 1.6 / 3.45 ms
cross-machine), coexisting with Apollo. Two real-hardware bugs the
GPU-less VM couldn't surface:

- DXGI capturer: the SudoVDA virtual monitor's DXGI output is enumerated
  under the GPU that *renders* it (the 4090, LUID 0x15df6), NOT under the
  SudoVDA "adapter" LUID SudoVDA reports (0x23276). Restricting the output
  search to that LUID found nothing → "adapter has no output named
  \\.\DISPLAYn". Now search ALL adapters for the GDI name, bind the D3D11
  device to whichever adapter exposes it (NVENC then shares that device),
  with a settle-retry (the output appears a beat after display creation)
  and topology logging.

- native_pairing / apps: keyed config paths off raw $HOME, which a Windows
  service/scheduled-task context doesn't set → "HOME unset" hard-fail at
  m3-host startup. Route both through gamestream::config_dir(), which falls
  back to %APPDATA% on Windows (cert/paired/apps now under AppData\Roaming).

clippy -D warnings + build green on x86_64-pc-windows-msvc (default and
--features nvenc) and Linux (78/78 tests).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/native_pairing.rs

@@ -7,7 +7,7 @@
 //! enters it (the client needs it to build its first message). So the UI **displays** the PIN —
 //! armed on demand for a short window — rather than accepting one.
 
-use anyhow::{Context, Result};
+use anyhow::Result;
 use std::path::PathBuf;
 use std::sync::Mutex;
 use std::time::{Duration, Instant};
@@ -101,8 +101,9 @@ pub struct NativePairingStatus {
 }
 
 fn default_path() -> Result<PathBuf> {
-    let home = std::env::var("HOME").context("HOME unset")?;
-    Ok(PathBuf::from(home).join(".config/punktfunk/punktfunk1-paired.json"))
+    // `config_dir()` resolves XDG/HOME on Linux and falls back to %APPDATA% on Windows — so the
+    // native paired-store works without a HOME env var (which a Windows service/task doesn't set).
+    Ok(crate::gamestream::config_dir().join("punktfunk1-paired.json"))
 }
 
 fn load(path: &std::path::Path) -> PairedClients {