Add SMTP security mode selector with SSL/STARTTLS/none options and automatic port switching

Replaced boolean `smtp_use_tls` with explicit `smtp_security` enum field supporting "none", "starttls", and "ssl" modes. Added database migration to create `smtp_security` column with "starttls" default. Updated mailer to use SMTP_SSL client for direct SSL connections on port 465 and SMTP with STARTTLS for port 587. Modified admin settings UI to show dropdown selector with encryption options and auto-adjust

frontend/src/components/AdminSettingsModal.jsx

@@ -7,7 +7,7 @@ import { useLanguage } from "../i18n";
 
 const initial = {
   smtp_host: "", smtp_port: 587, smtp_username: "", smtp_password: "",
-  smtp_from_email: "", smtp_from_name: "Cluedo HP", smtp_use_tls: true,
+  smtp_from_email: "", smtp_from_name: "Cluedo HP", smtp_security: "starttls",
   app_base_url: window.location.origin,
 };
 
@@ -72,7 +72,11 @@ export default function AdminSettingsModal({ open, onClose }) {
             <label style={styles.adminFieldLabel}>{t("senderName")}<input value={form.smtp_from_name} onChange={(e) => setField("smtp_from_name", e.target.value)} style={styles.input} /></label>
           </div>
           <label style={styles.adminFieldLabel}>{t("appUrl")}<input value={form.app_base_url} onChange={(e) => setField("app_base_url", e.target.value)} placeholder="https://notizbogen.example.com" style={styles.input} /></label>
-          <label className="hp-admin-check"><input type="checkbox" checked={!!form.smtp_use_tls} onChange={(e) => setField("smtp_use_tls", e.target.checked)} /> {t("useTls")}</label>
+          <label style={styles.adminFieldLabel}>{language === "en" ? "SMTP encryption" : "SMTP-Verschlüsselung"}<select value={form.smtp_security || "starttls"} onChange={(e) => { const security = e.target.value; setField("smtp_security", security); if (security === "ssl" && String(form.smtp_port) === "587") setField("smtp_port", 465); if (security === "starttls" && String(form.smtp_port) === "465") setField("smtp_port", 587); }} style={styles.input}>
+            <option value="none">{language === "en" ? "None" : "Keine Verschlüsselung"}</option>
+            <option value="starttls">STARTTLS</option>
+            <option value="ssl">{language === "en" ? "TLS/SSL (direct, port 465)" : "TLS/SSL (direkt, Port 465)"}</option>
+          </select></label>
           <div className="hp-settings-test">
             <label style={{ ...styles.adminFieldLabel, flex: 1 }}>{t("testEmail")}<input type="email" value={recipient} onChange={(e) => setRecipient(e.target.value)} placeholder="you@example.com" style={styles.input} /></label>
             <button onClick={test} style={styles.secondaryBtn} disabled={testing}>{testing ? (language === "en" ? "Sending …" : "Sende …") : t("sendTest")}</button>