feat(mcap): switch single-source exports to copy layout

Namespace single-source zed_svo_to_mcap outputs with a derived camera label so one-camera exports use the same copy-layout topic shape as current multi-camera copy files.

Use the per-camera frame and pose reference identifiers for those single-source outputs, document copy as the current one-camera wire shape, and clarify that legacy /camera/* files are retained only as a legacy contract.

Add a small mcap_rgbd_example helper plus mcap_recipes guide for summarizing bundled/copy MCAPs and exporting one RGB/depth sample, and update the validator and viewer wording/behavior to match the bundled-vs-copy semantics.

scripts/mcap_rgbd_viewer.py

@@ -975,7 +975,7 @@ class ViewerApp:
         with dpg.window(tag="main_window", label="MCAP RGBD Viewer", no_close=True):
             dpg.add_text(default_value="", tag="viewer_title")
             with dpg.group(horizontal=True):
-                if self.layout_info.layout != "single-camera":
+                if len(self.layout_info.camera_labels) > 1:
                     dpg.add_combo(
                         items=list(self.layout_info.camera_labels),
                         default_value=self.state.camera_label,