docs: document PWA and branding env vars in .env.example

Reorganize the Branding section with subsections (App identity, Icons &
favicon, PWA appearance, Logos, Login page) and document the new variables
APP_SHORT_NAME, APP_DESCRIPTION, PWA_ICON_URL, PWA_THEME_COLOR and
PWA_BACKGROUND_COLOR.

.env.example

@@ -6,7 +6,7 @@
 # JMAP Server (required)
 # =============================================================================
 
-# App name displayed in the UI
+# App name displayed in the UI, browser tab title, and PWA manifest.
 APP_NAME=Bulwark Webmail
 
 # URL of your JMAP-compatible mail server (required unless ALLOW_CUSTOM_JMAP_ENDPOINT is set)
@@ -106,41 +106,81 @@ JMAP_SERVER_URL=https://your-jmap-server.com
 # Branding (all optional)
 # =============================================================================
 
-# Custom favicon for the browser tab.
+# ---------------------------------------------------------------------------
+# App identity
+# ---------------------------------------------------------------------------
+
+# Short name for the app, used in contexts where space is limited
+# (e.g. home screen label on mobile). Defaults to APP_NAME if not set.
+# APP_SHORT_NAME=Bulwark
+
+# Description shown in the PWA manifest (displayed by the OS during install).
+# Defaults to a generic Bulwark description if not set.
+# APP_DESCRIPTION=Your personal webmail
+
+# ---------------------------------------------------------------------------
+# Icons & favicon
+# ---------------------------------------------------------------------------
+
+# Custom favicon shown in the browser tab.
 # Supported formats: SVG (recommended), PNG, ICO.
-# Recommended size: 32×32px minimum, 512×512px maximum (or SVG for best scaling).
+# Can be an absolute URL (https://...) or a path relative to the public/ directory.
-# Can be an absolute URL or a path relative to the public/ directory.
 # Defaults to the Bulwark favicon if not set.
 # FAVICON_URL=/branding/my-favicon.svg
 
-# Custom logos for the sidebar (shown in the main app after login).
+# Source image used to auto-generate PWA icons (192×192 and 512×512 PNG).
+# Supported formats: SVG (recommended for best quality) or PNG (≥512×512px recommended).
+# Can be an absolute URL (https://...) or a path relative to the public/ directory.
+# Falls back to FAVICON_URL if not set, and to the default Bulwark icons if neither is set.
+# PWA_ICON_URL=/branding/my-icon.svg
+
+# ---------------------------------------------------------------------------
+# PWA appearance
+# ---------------------------------------------------------------------------
+
+# Color applied to the browser UI chrome when the app is installed as a PWA
+# (address bar, status bar on Android). Default: #ffffff
+# PWA_THEME_COLOR=#3b82f6
+
+# Background color shown on the PWA splash screen while the app is loading.
+# Should match your app's main background color. Default: #ffffff
+# PWA_BACKGROUND_COLOR=#ffffff
+
+# ---------------------------------------------------------------------------
+# Logos
+# ---------------------------------------------------------------------------
+
+# Logos shown in the sidebar (main app, after login).
 # Supported formats: SVG (recommended), PNG, WebP.
-# Recommended size: min 24×24px, max 128×128px
+# Recommended size: min 24×24px, max 128×128px.
 # Can be absolute URLs or paths relative to the public/ directory.
 # If not set, no logo is shown in the sidebar.
 # APP_LOGO_LIGHT_URL=/branding/my-logo-color.svg
 # APP_LOGO_DARK_URL=/branding/my-logo-white.svg
 
-# Custom logo images for the login page.
+# Logos shown on the login page.
 # Supported formats: SVG (recommended), PNG, WebP.
-# Recommended size: min 32×32px, max 512×512px
+# Recommended size: min 32×32px, max 512×512px.
 # Can be absolute URLs or paths relative to the public/ directory.
-# Light mode logo (shown on light backgrounds), defaults to Bulwark logo.
+# Light mode logo (shown on light backgrounds). Defaults to the Bulwark logo.
 LOGIN_LOGO_LIGHT_URL=/branding/Bulwark_Logo_Color.svg
-#
+# Dark mode logo (shown on dark backgrounds). Defaults to the Bulwark white logo.
-# Dark mode logo (shown on dark backgrounds), defaults to Bulwark white logo.
 LOGIN_LOGO_DARK_URL=/branding/Bulwark_Logo_Color.svg
 
-# Company or organization name displayed above the version on the login page
+# ---------------------------------------------------------------------------
+# Login page
+# ---------------------------------------------------------------------------
+
+# Organization name shown above the version number on the login page.
 LOGIN_COMPANY_NAME=Bulwark Webmail
 
-# URL for the imprint/legal notice link on the login page
+# URL for the imprint / legal notice link on the login page.
 # LOGIN_IMPRINT_URL=https://example.com/imprint
 
-# URL for the privacy policy link on the login page
+# URL for the privacy policy link on the login page.
 # LOGIN_PRIVACY_POLICY_URL=https://example.com/privacy
 
-# URL for the company website link on the login page
+# URL for the organization website link on the login page.
 LOGIN_WEBSITE_URL=https://bulwarkmail.org
 
 # =============================================================================