feat(m28+m29+m30): ACME ARI, email digest, and Helm chart

M28: ACME Renewal Information (RFC 9702) — CA-directed renewal timing
with cert ID computation, directory endpoint discovery, graceful
degradation for non-ARI CAs. 19 tests.

M29: Email notifier wiring + scheduled certificate digest — SMTP
connector bridged to service layer via NotifierAdapter, DigestService
with HTML email template, 7th scheduler loop (24h), digest preview/send
API endpoints and GUI card. 21 tests.

M30: Production-ready Helm chart — server Deployment, PostgreSQL
StatefulSet, agent DaemonSet, ConfigMaps, Secrets, Ingress, security
contexts, health probes, example values for dev/prod/ACME scenarios.

Also: OpenAPI spec updates, MCP tool additions, CI helm-lint job,
documentation updates across 5 doc files and README.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/connector/notifier/email/email.go

@@ -195,6 +195,73 @@ func (c *Connector) sendEmail(ctx context.Context, to, subject, body string) err
 	return nil
 }
 
+// sendHTMLEmail sends an HTML email message using the configured SMTP server.
+// Used by the digest service for rich HTML digest emails.
+func (c *Connector) sendHTMLEmail(ctx context.Context, to, subject, htmlBody string) error {
+	addr := net.JoinHostPort(c.config.SMTPHost, strconv.Itoa(c.config.SMTPPort))
+
+	var auth smtp.Auth
+	if c.config.Username != "" && c.config.Password != "" {
+		auth = smtp.PlainAuth("", c.config.Username, c.config.Password, c.config.SMTPHost)
+	}
+
+	var conn net.Conn
+	var err error
+
+	if c.config.UseTLS {
+		tlsConfig := &tls.Config{
+			ServerName: c.config.SMTPHost,
+		}
+		conn, err = tls.Dial("tcp", addr, tlsConfig)
+		if err != nil {
+			return fmt.Errorf("failed to connect via TLS: %w", err)
+		}
+	} else {
+		conn, err = net.Dial("tcp", addr)
+		if err != nil {
+			return fmt.Errorf("failed to connect: %w", err)
+		}
+	}
+	defer conn.Close()
+
+	client, err := smtp.NewClient(conn, c.config.SMTPHost)
+	if err != nil {
+		return fmt.Errorf("failed to create SMTP client: %w", err)
+	}
+	defer client.Close()
+
+	if auth != nil {
+		if err := client.Auth(auth); err != nil {
+			return fmt.Errorf("SMTP authentication failed: %w", err)
+		}
+	}
+
+	if err := client.Mail(c.config.FromAddress); err != nil {
+		return fmt.Errorf("failed to set sender: %w", err)
+	}
+
+	if err := client.Rcpt(to); err != nil {
+		return fmt.Errorf("failed to set recipient: %w", err)
+	}
+
+	wc, err := client.Data()
+	if err != nil {
+		return fmt.Errorf("failed to get data writer: %w", err)
+	}
+	defer wc.Close()
+
+	message := c.formatHTMLEmailMessage(c.config.FromAddress, to, subject, htmlBody)
+	if _, err := wc.Write(message); err != nil {
+		return fmt.Errorf("failed to write message: %w", err)
+	}
+
+	if err := client.Quit(); err != nil {
+		return fmt.Errorf("failed to quit SMTP: %w", err)
+	}
+
+	return nil
+}
+
 // formatEmailMessage formats an email message with standard headers.
 func (c *Connector) formatEmailMessage(from, to, subject, body string) []byte {
 	message := fmt.Sprintf(
@@ -208,6 +275,19 @@ func (c *Connector) formatEmailMessage(from, to, subject, body string) []byte {
 	return []byte(message)
 }
 
+// formatHTMLEmailMessage formats an HTML email message with MIME headers.
+func (c *Connector) formatHTMLEmailMessage(from, to, subject, htmlBody string) []byte {
+	message := fmt.Sprintf(
+		"From: %s\r\nTo: %s\r\nSubject: %s\r\nDate: %s\r\nMIME-Version: 1.0\r\nContent-Type: text/html; charset=utf-8\r\n\r\n%s",
+		from,
+		to,
+		subject,
+		time.Now().Format(time.RFC1123Z),
+		htmlBody,
+	)
+	return []byte(message)
+}
+
 // formatAlertBody formats an alert notification as email body text.
 func (c *Connector) formatAlertBody(alert notifier.Alert) string {
 	body := fmt.Sprintf(`