feat(mcap): add copy mode for multi-camera exports

Add an opt-in multi-camera copy layout for zed_svo_to_mcap.

copy mode preserves each camera's original timestamps and cadence,
writes namespaced /zedN topics without /bundle, and supports
common-overlap or full-range export windows.

Update the batch wrapper, Python validator, RGBD viewer, and
documentation so copy-layout MCAP files are treated as a first-class
format rather than invalid bundled output.

Validation:
- cmake --build build --target zed_svo_to_mcap -j4
- uv run python -m py_compile scripts/zed_batch_svo_to_mcap.py scripts/mcap_bundle_validator.py scripts/mcap_rgbd_viewer.py
- build/bin/zed_svo_to_mcap --segment-dir /workspaces/data/kindergarten/bar/2026-03-18T11-59-41 --output /tmp/bar_11-59-41_copy_common.mcap --encoder-device nvidia --depth-mode neural_plus --depth-size optimal --bundle-policy copy --copy-range common
- uv run python scripts/mcap_bundle_validator.py /tmp/bar_11-59-41_copy_common.mcap
- uv run --extra viewer python scripts/mcap_rgbd_viewer.py /tmp/bar_11-59-41_copy_common.mcap --summary-only

pyproject.toml

@@ -12,5 +12,11 @@ dependencies = [
     "zstandard>=0.23",
 ]
 
+[project.optional-dependencies]
+viewer = [
+    "dearpygui>=2.2",
+    "rvl-impl @ git+https://github.com/crosstyan/rvl-impl.git@74308bcaf184cb39428237e8f4f99a67a6de22d9 ; python_version >= '3.12'",
+]
+
 [tool.uv]
 package = false