Move email types to pkg/email for cloud repo access

Extracts Mailer interface, EmailData, and Button to pkg/email/types.go
so the cloud repo can use them via ServerContext. internal/email re-exports
the types as aliases so existing callers are unchanged. Also fixes
pre-existing lint errors (unchecked rollback and deadline calls).

pkg/email/types.go

@@ -0,0 +1,27 @@
+// Package email defines the public types for transactional email sending.
+// The implementation lives in internal/email — this package only exposes
+// the interface and data types so the cloud repo can use them via ServerContext.
+package email
+
+import "context"
+
+// Mailer sends transactional emails.
+type Mailer interface {
+	Send(ctx context.Context, to string, subject string, data EmailData) error
+}
+
+// EmailData is the generic payload for all transactional emails.
+// Templates conditionally render each field based on presence.
+type EmailData struct {
+	RecipientName string  // optional — used after "Hello"
+	Message       string  // main body (plain text; HTML template wraps it)
+	Button        *Button // optional CTA button
+	Closing       string  // optional closing/footer message
+}
+
+// Button represents a call-to-action link rendered as a button in HTML
+// and as a plain URL in the text variant.
+type Button struct {
+	Text string // button label
+	URL  string // target URL
+}