Some broadcasting software (e.g., Prism Live Studio) strips special
characters from stream keys, making Owncast-generated keys incompatible.
Changes:
- Create separate STREAM_KEY_COMPLEXITY_RULES without special char requirement
- Update generateRndKey() to only use alphanumeric characters
- Keep PASSWORD_COMPLEXITY_RULES unchanged for admin password security
- Update tooltip text to reflect new requirements
- Add comprehensive tests for stream key generation
Fixes#4690
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>