fix: Event frontmatter YAML injection — use yaml.safe_dump for construction #23

What to build

EventEmitter._persist_event manually constructs YAML frontmatter with f'{key}: "{val}"'. If val contains colons, quotes, or backslashes, the output is invalid YAML.

Use yaml.safe_dump for the entire frontmatter dict instead of manual line construction.

Acceptance criteria

• Frontmatter is valid YAML for all input values
• Tests verify special characters in event fields produce valid YAML

Blocked by

None - can start immediately

Parent

Tracks the campus framework v1 code review: #27