BowEcho v0.27.3

This hotfix improves live US Level II radar freshness when the realtime
Unidata chunk bucket contains stale or reused volume-ID prefixes.

Live Radar / Level II

Fixed stale realtime chunk selection for US radars when old high-numbered
chunk directories remain in unidata-nexrad-level2-chunks.
BowEcho now rescans actual chunk object timestamps when the ID-based
realtime pick is stale, so fresh lower-numbered reused IDs like the KLNX
case are selected correctly.
Fixed reused chunk volume IDs being grouped only by ID. Chunks are now
separated by both volume ID and embedded volume time, preventing mixed-volume
realtime files.
Added fallback behavior so if realtime chunks are still stale, AutoRefresh
can fall through to the current completed Level II volume instead of treating
the stale realtime result as unchanged.
Added regression coverage for stale high IDs, reused-ID chunk mixing, and the
app-side stale-realtime fallback path.
Added an ignored live KLNX resolver smoke test for checking the public
realtime chunk bucket directly.

cargo fmt --all --check
cargo test -p data_source realtime_chunk_scan --quiet
cargo test -p data_source latest_realtime_level2_volume_live_klnx -- --ignored --nocapture
cargo test -p app_ui stale_realtime_chunks_trigger_archive_fallback --quiet
cargo check -p data_source
cargo check -p app_ui --bin bowecho
git diff --check
cargo build -p app_ui --bin bowecho --release