Follow-up to #1126 (which closed the HTML-injection vector in the Body).
The Subject line is not HTML-rendered, so html.EscapeString would leak
literal entities into recipient inboxes. Instead:
- Strip control characters from workspace/inviter names (defense in depth
even though Resend also filters CR/LF).
- Cap each field at 60 runes so an attacker can't stuff a full phishing
pitch into a workspace name that gets sent from noreply@multica.ai.
Also extracts buildInvitationParams to make the sanitization logic
testable without mocking the Resend SDK, and adds a test covering:
- HTML escape behavior for script/attribute/anchor injection payloads
- Subject stripping of \r\n\t and other unicode controls
- Subject NOT being HTML-escaped (so "Acme & Co." stays literal)
- Subject length bounds
- Benign inputs pass through unchanged
Adds a note on SendVerificationCode that its body uses only
server-generated content, to prevent the same pitfall from creeping in.
Refs #1117
