New

• api,sdk: accept string or array for email `to` field
• api: add /.well-known/security.txt (RFC 9116)
• api: add signup forms CRUD API and embeddable JS widget
• api: add suppression bulk import and CSV export
• dashboard: add dedicated sending IP admin UI
• dashboard: add send test email button to overview page
• docs: add quickstart guide with all 4 SDK examples
• implement remaining issues (,,,) #300
• landing: add Go SDK example and documentation links
• sdk: add missing API methods, fix response deserialization, add examples
• sdk: add signup form methods to all 4 SDKs
• smtp,dashboard: add SMTP headers and quota exceeded warnings #299
• worker: add IP warmup auto-progression with bounce monitoring

Fixed

• dashboard: apply format_datetime filter to raw timestamps in template list and version history
• sdk: add HTTP timeout, HTTPS enforcement, and Python lockfile
• sdk: update Rust SDK tests for Recipient type and API envelope