fix(electron): real VNCmail+ branding, not just a rename

Every prior distributable DMG this session was built with plain `npx
electron-builder`, never `--config electron-builder.config.js`. electron-
builder does not auto-detect a file named electron-builder.config.js (its
search list is .yml/.yaml/.json/.json5/.js/.cjs/.mjs/.ts, not .config.js),
so the config - correct productName/appId/icon and all - was silently
ignored on every build. Caught only by actually launching the packaged
.app: it booted to "Bulwark Webmail Setup" demanding a token from
container logs, default Electron atom icon, output in dist/ instead of
dist-electron-builds/.

Fixes, each verified against the packaged .app (Playwright _electron.launch,
not the build log):
- Add dist:mac/win/linux/dir scripts that pass --config explicitly, so this
  can't recur.
- Dedicated 1024x1024 app icon (build-resources/app-icon.png, SRC symbol on
  #09090b) instead of reusing the web PWA manifest icon. Verified: icns
  ships at 1024x1024, pixel-identical to the source (mean diff 0.0/255).
- electron/main.ts: getDesktopDefaults() sets JMAP_SERVER_URL to the sandbox
  (the ONLY thing that puts the server into "env-managed" mode and skips
  the setup wizard - see lib/setup/state.ts), plus APP_NAME/login logo/
  favicon/company-name env vars, spread before ...process.env so a real
  deployment still overrides. Verified: packaged app now opens straight to
  a login screen with the JMAP endpoint field pre-filled
  https://stalwart.sandbox.vnc.de, title "VNCmail+", SRC logo.
- LOGIN_SHOW_SUBTITLE=false: the subtitle falls back to the login.title
  i18n string ("Webmail") whenever it differs from APP_NAME - a check
  written for the original Bulwark pairing where they matched. Hiding it
  avoids touching that shared string for every other deployment.

electron/main.ts

@@ -70,6 +70,51 @@ function getServerDataDirs(): Record<string, string> {
   };
 }
 
+/**
+ * Desktop-shell defaults for a fresh, un-configured install.
+ *
+ * Setting JMAP_SERVER_URL puts the standalone server into "env-managed"
+ * mode (see lib/setup/state.ts's detectSetupState()) - the ONLY thing that
+ * disables the setup wizard short of an operator finishing it by hand. Every
+ * distributable build of this desktop shell up to 2026-08-05 skipped this,
+ * so handing someone the packaged app landed them on "Bulwark Webmail
+ * Setup" asking for a token out of container logs they have no access to -
+ * caught only by actually launching the packaged .app and looking, not by
+ * reading the build log.
+ *
+ * The rest are CONFIG_ENV_MAP entries (lib/admin/types.ts) that only matter
+ * while env-managed - once an admin completes the wizard, config.json wins
+ * for everything except jmapServerUrl itself. allowCustomJmapEndpoint keeps
+ * the server field on the login screen editable, so this is a starting
+ * point for the sandbox, not a hard lock to it.
+ *
+ * `...process.env` in startStandaloneServer() below is spread AFTER this
+ * object, so a real deployment env (the Dockerfile path, or a future
+ * per-install override) still wins over these defaults.
+ */
+function getDesktopDefaults(): Record<string, string> {
+  return {
+    JMAP_SERVER_URL: "https://stalwart.sandbox.vnc.de",
+    APP_NAME: "VNCmail+",
+    APP_SHORT_NAME: "VNCmail+",
+    LOGIN_LOGO_LIGHT_URL: "/branding/SRC_Symbol.png",
+    LOGIN_LOGO_DARK_URL: "/branding/SRC_Symbol.png",
+    LOGIN_COMPANY_NAME: "VNC AG",
+    FAVICON_URL: "/branding/SRC_Symbol.png",
+    ALLOW_CUSTOM_JMAP_ENDPOINT: "true",
+    // The login page's subtitle falls back to the login.title i18n string
+    // whenever it differs from appName (app/(main)/[locale]/login/page.tsx)
+    // - a check clearly written for the original Bulwark/"Webmail" pairing,
+    // where they matched. With APP_NAME overridden to "VNCmail+" they no
+    // longer match, so the raw translation ("Webmail") surfaces instead of
+    // anything brand-appropriate. Hiding the subtitle avoids editing a
+    // shared i18n string that every other deployment (incl. Bulwark
+    // default) still uses - the SRC logo + "VNCmail+" heading is enough
+    // context on its own.
+    LOGIN_SHOW_SUBTITLE: "false",
+  };
+}
+
 /**
  * Locates the standalone server's entrypoint. Packaged builds ship it as an
  * extraResource (see electron-builder.config.js) because .next/standalone
@@ -156,6 +201,10 @@ async function startStandaloneServer(): Promise<string> {
   // what travels over it is.
   serverProcess = spawn(process.execPath, [serverEntry], {
     env: {
+      // First, so any real deployment env (a future per-install override,
+      // or this same binary run somewhere JMAP_SERVER_URL is already set)
+      // wins over these desktop-shell defaults - see getDesktopDefaults().
+      ...getDesktopDefaults(),
       ...process.env,
       ELECTRON_RUN_AS_NODE: "1",
       PORT: String(port),