fix image preview and add option for automatically stop auto screenshoting when idle

shared/mc-api/src/main/java/dev/photosync/mcapi/GameContext.java

@@ -1,6 +1,9 @@
 package dev.photosync.mcapi;
 
+import dev.photosync.core.capture.CameraPose;
+
 import java.nio.file.Path;
+import java.util.Optional;
 
 /** The ambient client state PhotoSync has to consult, and the render thread. */
 public interface GameContext {
@@ -11,6 +14,18 @@ public interface GameContext {
     /** True while any screen is up, vanilla's or ours. Automatic capture checks this. */
     boolean screenOpen();
 
+    /**
+     * Where the camera is and which way it faces, or empty when there is nothing
+     * to be looking through -- the title screen, or a world that is still
+     * loading.
+     *
+     * <p>Sampled every tick by the automatic-capture timer, which uses it to tell
+     * an idle player apart from one who is actually somewhere new. Nothing else
+     * needs it, and nothing should read a Minecraft position through it: it is
+     * deliberately a snapshot of five numbers rather than a handle on an entity.
+     */
+    Optional<CameraPose> cameraPose();
+
     /** {@code .minecraft/config}, where PhotoSync keeps its settings and upload queue. */
     Path configDirectory();