Implement bundled multi-camera --start-frame semantics as synced-group\nindices from the common synced start, inclusive with --end-frame.\n\nUpdate zed_svo_to_mcap to skip synced groups before writing, keep\nsingle-camera raw SVO frame semantics unchanged, and adjust exact\nprogress totals for selected bundled windows.\n\nReplace the expensive bundled exact pre-count path with approximate\ntime-window progress when --end-frame is not set, and update the\nshared TTY progress bar helper to support fraction-based rendering.\n\nExpose --start-frame in the batch MCAP wrapper and document the\nbundled frame-window semantics and approximate progress behavior in\nthe README.
Extract the tqdm-like stderr progress bar into a shared helper and reuse it across zed_svo_to_mp4, zed_svo_grid_to_mp4, and zed_svo_to_mcap.
For zed_svo_to_mcap, single-source exports now report exact frame totals and bundled multi-camera exports report exact synced-group totals on TTY. When bundled mode runs without --end-frame, the tool performs a counting pass first so the progress total remains exact instead of estimated.
Also document the bundled MCAP progress behavior in the README and record the current third_party dependency state in third_party/README. That note now makes it explicit that CLI11 and proxy are the active submodules, while tomlplusplus and mcap are vendored source drops, and adds a TODO to revisit converting mcap into a submodule later.
Verified with the Debug build during implementation, including single-camera and bundled zed_svo_to_mcap runs that rendered clean progress output to a TTY.
crosstyan