Estimate and invoice emails route replies directly to sender

Customer replies to estimates or invoices now land in the sender's inbox instead of a generic contact address.

Bug Fixes

Estimate and invoice emails now set the Reply-To header to the sending user's email address. When a client hits Reply, their message lands directly in that user's inbox instead of a generic org contact. This closes the loop on customer conversations.

As a bonus, the From address switched from noreply@ to info@ to improve email deliverability — major email providers penalize no-reply addresses for signaling one-way communication.