Render continuously and optimize the glTF viewer

Remove vsync and dirty-flag frame gating, optimize PBR sampling and lighting, add a direct-to-canvas loadout, and preserve camera state on viewer resize.

Add regression coverage and update rendering documentation.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b382-1e79-712b-abd1-d29201c9bb5e
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

core/render_data.rs

@@ -108,7 +108,6 @@ impl RenderData {
             pending: HashMap::new(),
         };
         data.create_rows("signals".into(), 1, 32, "f32".into())?;
-        data.write_signal(5, 1.0);
         Ok(data)
     }
 
@@ -321,25 +320,13 @@ impl RenderData {
         }
     }
 
-    pub fn render_pending(&self) -> bool {
-        self.signal(4) == 0.0 && self.signal(5) != 0.0 && self.signal(6) == 0.0
-    }
-
-    pub fn begin_render(&mut self) -> bool {
-        if !self.render_pending() {
-            return false;
-        }
-        self.write_signal(5, 0.0);
-        true
-    }
-
-    pub fn mark_dirty(&mut self) {
-        self.write_signal(5, 1.0);
+    pub fn render_allowed(&self) -> bool {
+        // Lane 5 (legacy dirty flag) no longer gates continuous rendering.
+        self.signal(4) == 0.0 && self.signal(6) == 0.0
     }
 
     pub fn loadout_ready(&mut self) {
         self.write_signal(6, 0.0);
-        self.mark_dirty();
     }
 
     fn signal(&self, index: usize) -> f32 {