fix(spike): --codec pyrowave encoded PyroWave off a capture negotiated for somebody else

Found while taking PW2's on-glass measurement, and it is what made the measurement possible.

`spike` built its capture request from `OutputFormat::resolve`, the constructor shared with the
GameStream path, which hard-codes `pyrowave: false` ("GameStream never negotiates PyroWave").
On Linux that flag is not cosmetic: `capture_virtual_output` feeds it to `zero_copy_policy` as
`ZeroCopyPolicy::pyrowave_session`, which is what puts the capture on the raw-dmabuf passthrough.
So `--codec pyrowave` opened a PyroWave encoder over a capture negotiated for a different
consumer, and the only way to exercise the real path was the host-global
`PUNKTFUNK_ENCODER=pyrowave` lever.

That lever cannot stand in for the per-session flag, which is the part that matters here: it
resolves the backend to `Pyrowave`, and `linux_zero_copy_is_vaapi_for` returns true for that —
so it ALSO flips `backend_is_vaapi` on. A per-session PyroWave negotiation on an auto/NVENC host,
where `backend_is_vaapi` is false, was therefore unreachable from the CLI — and that is exactly
the configuration whose CPU downgrade logged nothing at all.

The spike now sets the flag from its own codec, the same comparison `session_plan::output_format`
makes for a real session. With it, the before/after on .21 is unambiguous: origin/main logs zero
capture-path lines on that configuration, this branch logs two (the resolved arm, and the named
downgrade with its cause and fix).

crates/punktfunk-host/src/spike.rs

@@ -114,9 +114,21 @@ pub fn run(opts: Options) -> Result<()> {
                     refresh_hz: opts.fps,
                 })
                 .context("create virtual output")?;
+            // `resolve` is the shared GameStream/spike constructor and hard-codes `pyrowave: false`
+            // (GameStream never negotiates it). The spike DOES know its codec, and on Linux that
+            // flag is what puts the capture on the raw-dmabuf passthrough
+            // (`ZeroCopyPolicy::pyrowave_session`, set from the same comparison in
+            // `session_plan::output_format`). Left false, `--codec pyrowave` encoded PyroWave off a
+            // capture negotiated for somebody else, and the only way to exercise the real path was
+            // the host-global `PUNKTFUNK_ENCODER=pyrowave` lever — which ALSO flips
+            // `backend_is_vaapi`, so it cannot reproduce a per-session PyroWave negotiation on an
+            // auto/NVENC host at all. That is precisely the configuration PW2 exists for.
+            let mut want =
+                capture::OutputFormat::resolve(false, crate::encode::resolved_backend_is_gpu());
+            want.pyrowave = opts.codec == Codec::PyroWave;
             capture::capture_virtual_output(
                 vout,
-                capture::OutputFormat::resolve(false, crate::encode::resolved_backend_is_gpu()),
+                want,
                 crate::session_plan::CaptureBackend::resolve(),
                 compositor == crate::vdisplay::Compositor::Kwin,
             )