Allow LiveKit regional CSP hosts

[jserv]

LiveKit Cloud can redirect a browser to a regional signaling host after the configured endpoint. Keep the corresponding Cloud wildcard beside the exact HTTP and WebSocket sources, while rejecting endpoint spellings that cannot safely appear in a CSP.

Closes #36

[alanhc]

Tests pass locally (205 unit tests).

The substantive change here is csp_origin, not the wildcard: the previous path went through url_origin alone, which only checks for printable ASCII, so a configured wss://host;script-src=* reached the header verbatim and the semicolon terminated connect-src early. Rejecting the endpoint and withholding its Cloud wildcard is the right call, and the test pins it.

Two notes:

• The host-character check would sit better in validate_livekit_url. As it stands a malformed host still starts the server and fails only in the browser, which is the shape of failure the rest of this file argues against.
• The _ => return vec![origin] arm in livekit_origins_for_csp_origin is now unreachable: every endpoint passes validate_livekit_url, so the scheme is one of the four.