PRJ-8: proxies — Set Proxy / None / Use Proxy / Create Proxy / Interpret Proxy, Proxy Use; PRJ-3 interpret fields, PAR, alpha guess

Items (footage and comps) carry a proxy rendered in their place at the source's size when
its switch and Render Settings > Proxy Use allow it; Create Proxy queues a half-resolution
render whose post-render action attaches it. Interpret Footage gains Separate Fields
(upper/lower first, fields become frames at twice the rate), Guess alpha with matte colour,
explicit matte colour, Invert Alpha, Interpret As Linear Light; non-square footage, solids
and precomps are stretched by their pixel aspect in the comp. The four proxy stubs are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/render_queue.rs

@@ -388,6 +388,11 @@ impl Session {
         }
         let importer = self.importer.clone().ok_or("media import is not available in this build")?;
         let footage = importer.probe(path)?;
+        if item.post_render == PostRenderAction::SetProxy {
+            crate::commands::proxy_set(self, item.comp, footage).map_err(|e| e.to_string())?;
+            self.toast(format!("Proxy set from {path}"));
+            return Ok(None);
+        }
         let name = std::path::Path::new(path).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_else(|| path.to_string());
         let replace = item.post_render == PostRenderAction::ImportAndReplace;
         let comp = item.comp;