feat(zed): add DuckDB segment timestamp indexer

Add a new mcap_video_bounds helper binary plus a zed_segment_time_index.py CLI that builds and queries an embedded DuckDB index for bundled ZED segment recordings.

The index stores segment folders, MCAP paths, video time bounds, durations, camera labels, and dataset metadata, and reuses the existing recursive multi-camera segment discovery logic so nested kindergarten layouts are indexed correctly.

Infer a dataset default timezone from folder names versus MCAP timestamps, and make point queries precision-aware so second-level folder timestamps like 2026-03-18T12-00-23 resolve to the matching segment instead of missing due to subsecond start offsets.

Verification:
- uv add 'duckdb>=1.0'
- cmake --build build --target mcap_video_bounds
- uv run python -m unittest tests.test_zed_segment_time_index
- uv run python scripts/zed_segment_time_index.py build /workspaces/data/kindergarten --jobs 8
- uv run python scripts/zed_segment_time_index.py query /workspaces/data/kindergarten --at 2026-03-18T12-00-23

uv.lock

@@ -33,6 +33,7 @@ version = "0.0.0"
 source = { virtual = "." }
 dependencies = [
     { name = "click" },
+    { name = "duckdb" },
     { name = "numpy", version = "2.2.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },
     { name = "numpy", version = "2.4.3", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
     { name = "opencv-python-headless" },
@@ -44,6 +45,7 @@ dependencies = [
 [package.metadata]
 requires-dist = [
     { name = "click", specifier = ">=8.1" },
+    { name = "duckdb", specifier = ">=1.0" },
     { name = "numpy", specifier = ">=2.2" },
     { name = "opencv-python-headless", specifier = ">=4.11" },
     { name = "progress-table", specifier = ">=3.2" },
@@ -51,6 +53,48 @@ requires-dist = [
     { name = "zstandard", specifier = ">=0.23" },
 ]
 
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