chore(windows): clean up build/packaging - drop vendored driver binaries + the LLVM-21 pin

Now that the drivers build from source in CI, remove the dead checked-in binaries and
the toolchain cruft they left behind:

- Delete packaging/windows/{pf-vdisplay,gamepad-drivers}/ (the prebuilt .dll/.inf/.cat/.cer).
  pack-host-installer.ps1 builds + signs all three drivers from the drivers/ workspace and
  nothing reads the vendored dirs anymore; stage-pf-vdisplay.ps1's -VendorDir is now a
  mandatory build-output path, not a vendored default.
- Drop the LLVM-21 pin. The vendored bindgen 0.71->0.72 bump (the shipping pack already
  builds green on the runner-default clang 22) retired the bindgen-0.71 layout-test overflow
  that needed LLVM 21.1.2, so windows-drivers.yml + provision-windows-wdk.ps1 no longer
  install/point at C:\llvm-21 (~898 MB off a fresh provision) - both driver builds now use one
  toolchain (clang 22 + bindgen 0.72).
- pack -SkipBuild on the gamepad build (build-pf-vdisplay.ps1 already builds the whole
  workspace), build-web.ps1 reaps a stale node too, deploy-dev.ps1 nefconc path + comments.
- Reword the vendored-driver references (build scripts, .iss, READMEs, the vite web-bundle
  comment) to the build-from-source reality.

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

.gitea/workflows/windows-drivers.yml

@@ -76,7 +76,7 @@ jobs:
           head "EWDK"
           Write-Host ("EWDKROOT = " + ($env:EWDKROOT ?? '<unset>'))
 
-          head "LLVM / clang (README pins 21.1.2 for wdk-sys bindgen)"
+          head "LLVM / clang (bindgen 0.72 builds on the runner default clang)"
           Write-Host ("LIBCLANG_PATH = " + ($env:LIBCLANG_PATH ?? '<unset>'))
           $clang = Get-Command clang -ErrorAction SilentlyContinue
           if ($clang) { & clang --version } else { Write-Host "clang: NOT on PATH" }
@@ -119,12 +119,12 @@ jobs:
     env:
       # wdk-build otherwise picks 10.0.28000.0 (no km/crt) and bindgen fails — pin the WDK SDK version.
       Version_Number: '10.0.26100.0'
-      # wdk-sys bindgen layout tests overflow (E0080) on the runner's default LLVM (ToT/22-dev); point at
-      # the pinned LLVM 21.1.2 that windows-drivers-rs builds clean against (provisioned to C:\llvm-21).
-      LIBCLANG_PATH: 'C:\llvm-21\bin'
+      # No LIBCLANG_PATH pin: the vendored bindgen 0.72 builds clean on the runner's default clang 22
+      # (the shipping pack proves it). A 0.71-era layout-test overflow once needed LLVM 21; the 0.72 bump
+      # retired that — see design/windows-build-and-packaging.md.
     steps:
       - uses: actions/checkout@v4
-      - name: Ensure WDK + cargo-wdk + LLVM 21.1.2 (idempotent self-provision)
+      - name: Ensure WDK + cargo-wdk (idempotent self-provision)
         # Run the provisioning script here too so driver-build is self-sufficient and never races a
         # separate provision run on the single runner. Path is relative to the job working-directory
         # (packaging/windows/drivers). Near-noop once the toolchain is present.