Extract emails into separate package with clean interface

- Create packages/emails/ with EmailClient interface abstraction
- Wrap Postmark ServerClient in adapter for clean typing
- Add createLoggingEmailClient for dev mode (logs to console)
- Split email templates into individual files with full test coverage
- Update api-server to use new package via context injection
- Remove EMAIL_DEV_MODE - now uses POSTMARK_API_KEY presence
- Delete apps/api-server/src/utils/email.ts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/emails/src/index.ts

@@ -0,0 +1,26 @@
+// Client factories
+export { createPostmarkClient } from "./client.js";
+export { createLoggingEmailClient } from "./logging-client.js";
+
+// Core types
+export type { EmailClient, EmailResult } from "./types.js";
+
+// Base send function
+export { sendEmail } from "./send.js";
+export type { SendEmailParams } from "./send.js";
+
+// Email-specific send functions
+export {
+  sendLoginConfirmationEmail,
+  sendOrgInviteEmail,
+  sendPasswordResetEmail,
+  sendVerificationEmail,
+} from "./emails/index.js";
+
+// Email param types
+export type {
+  SendLoginConfirmationEmailParams,
+  SendOrgInviteEmailParams,
+  SendPasswordResetEmailParams,
+  SendVerificationEmailParams,
+} from "./emails/index.js";