feat(host/linux): NVIDIA clock hygiene — P2-cap driver profile + opt-in NVML clock floor

Two halves of the easy-scene p99 lever (host-latency plan Tier 1B):
CudaNoStablePerfLimit application profile (no root; NVIDIA's supported
opt-out of the CUDA/NVENC P2 memory-clock clamp, raw key 0x166c5e=0 per
open-gpu-kernel-modules#333, shipped for obs/Discord in R595) installed
into ~/.nv/nvidia-application-profiles-rc.d/ keyed on procname, opt-out
PUNKTFUNK_NV_PROFILE=0; and PUNKTFUNK_PIN_CLOCKS=1 arming an NVML
SetGpuLockedClocks(TDP, UNLIMITED) core-clock floor (base floor, boost
headroom — never a max pin) held for the host lifetime, reset-on-start
self-healing a crashed run's stale pin, NO_PERMISSION degrading to a
logged sudoers/oneshot recipe. libnvidia-ml is dlopen'd like libcuda —
no link-time dependency, clean no-op off NVIDIA.

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

crates/punktfunk-host/src/main.rs

@@ -45,6 +45,9 @@ mod library;
 mod mgmt;
 mod mgmt_token;
 mod native_pairing;
+#[cfg(target_os = "linux")]
+#[path = "linux/nvclocks.rs"]
+mod nvclocks;
 mod pipeline;
 mod punktfunk1;
 mod pwinit;
@@ -127,6 +130,15 @@ fn real_main() -> Result<()> {
     #[cfg(target_os = "windows")]
     crate::capture::dxgi::install_gpu_pref_hook();
 
+    // NVIDIA clock hygiene (Linux, host subcommands only): install the P2-cap driver profile and,
+    // under PUNKTFUNK_PIN_CLOCKS, hold the NVML core-clock floor for the host lifetime (reset on
+    // exit via the guard's Drop). No-op off NVIDIA / on the tool subcommands.
+    #[cfg(target_os = "linux")]
+    let _nv_clocks = match args.first().map(String::as_str) {
+        Some("serve") | Some("punktfunk1-host") => nvclocks::on_host_start(),
+        _ => None,
+    };
+
     match args.first().map(String::as_str) {
         // The host: the native punktfunk/1 plane + management API by default (secure), and — with
         // --gamestream — the GameStream/Moonlight-compat planes too (opt-in; #5/#9 trusted-LAN caveat).