Address three P1 code review comments on PR #3352:
1. Colon-separator bypass: parseSlashCommand() treats ':' as an argument
separator, but shouldSkipHistory only split on whitespace. So
/login:?code=abc&state=xyz bypassed the filter. Now uses the same
earliest-whitespace-or-colon splitting as parseSlashCommand.
2. /join <link> secret: the collab join link carries a 32-byte room key
and optional write token. Add /join to the denylist — skip any /join
with arguments.
3. Added regression tests for colon-separator forms and /join denylist.
oldschoola
00fd6f2263