multicam: no-split switch skips full rebuild, angle refresh stride, proxy in node-graph decode

- multicam_switch_to: a NO-SPLIT switch only changes current source —
  push snapshot + invalidate preview windows, skip the full
  apply_edit rebuild (the 'switch once then everything grinds' hit)
- MulticamPanel: playback angle refresh runs one cycle per 3 ticks
  instead of re-requesting every source every tick (each angle decode
  is a keyframe-scanning FFmpeg seek)
- footage value(): a ready proxy stands in for the original media in
  the node-graph decode request (proxy enabled but 4K decoded report)
- proxy_resolution made public (engine's proxy-first preview size)

crates/oak-node/src/footage.rs

@@ -25,6 +25,13 @@ use crate::input::Input;
 use crate::node::{Category, NodeBehavior, NodeCore};
 use crate::value::{AudioParams, NodeValue, NodeValueRow, NodeValueTable, ValueType, VideoParams};
 
+/// Whether the footage's proxy state value means "the proxy file is
+/// ready on disk" (the C++ `ProxyState::Ready` = 2; the footage behavior
+/// stores it raw to avoid a codec-crate dependency here).
+pub(crate) fn proxymanager_proxy_state_ready(state: i32) -> bool {
+	state == 2
+}
+
 /// One media stream inside a footage file.
 #[derive(Clone, Debug)]
 pub struct StreamInfo {
@@ -351,6 +358,13 @@ impl NodeBehavior for FootageBehavior {
 	/// boxed [`crate::nodes::jobs::FootageJobPayload`] the render hooks
 	/// resolve to the decoded frame. A footage with no probed video stream
 	/// (or no filename) outputs nothing.
+	///
+	/// A ready proxy stands in for the original media (the node-graph
+	/// renderer's counterpart of the montage path's proxy selection): the
+	/// payload then names the proxy file/stream instead of the 4K
+	/// original — without this the node-graph preview decodes full
+	/// resolution even with proxies enabled (the "proxy on but preview is
+	/// still 4K and the GPU crawls" report).
 	fn value(
 		&self,
 		_core: &NodeCore,
@@ -364,9 +378,23 @@ impl NodeBehavior for FootageBehavior {
 		let Some(stream) = self.streams.iter().find(|s| s.is_video) else {
 			return;
 		};
+		// Proxy selection mirrors the montage path's
+		// `preview_footage_media`: enabled + Ready state, and the proxy
+		// replaces the first video stream only (C++ matches the proxy's
+		// video stream index against the footage's first video stream).
+		let proxy_ready = proxymanager_proxy_state_ready(self.proxy_state);
+		let use_proxy = self.proxy_enabled
+			&& !self.proxy.is_empty()
+			&& proxy_ready
+			&& self.proxy_video_stream_index == stream.index;
+		let (filename, stream_index) = if use_proxy {
+			(self.proxy.clone(), 0)
+		} else {
+			(self.filename.clone(), stream.index)
+		};
 		let payload = crate::nodes::jobs::FootageJobPayload {
-			filename: self.filename.clone(),
-			stream_index: stream.index,
+			filename,
+			stream_index,
 			time,
 		};
 		table.push(