Consolidate the two stream-check tools into a single master script with
three subcommands:
- check <url> verify one stream (or --live dashboard)
- playlist <path|url> batch an .m3u list -> aggregate JSON (+ per-stream files)
- graph <inputs...> render the JSON as SVG charts
Shared helpers (HTTP, slugify, m3u/JSON handling) are now defined once.
The old --playlist flag becomes the `playlist` subcommand and the bare-URL
form becomes `check <url>`; the streamtest harness is updated accordingly.
Also fix the per-stream SVG rendering black in viewers that do not support
8-digit #rrggbbaa hex: the bitrate area fill and not-PLAYING bands now use
6-digit hex plus a separate fill-opacity attribute.
Docs (English + tools READMEs + STREAMTEST) updated to the new invocation.
Removes stream_queue_check.py and stream_graph.py.
