feat(glass): user-facing Image-fade slider under Settings > Background image

Replaces the dev-only backdrop-fade knob with a real control: when Background
image is on (dark theme), a 0-100% 'Image fade' slider appears beneath it and
drives --bg-fade live (higher = fainter). Persists to DB + localStorage via the
existing theme prefs path (ThemePrefs.bgFade, applyTheme sets the CSS var).
Removed --bg-fade from the GlassTuner so the two don't fight over the var.

frontend/src/components/GlassTuner.tsx

@@ -38,7 +38,6 @@ const SLIDERS: Slider[] = [
   { k: "--glass-inset", label: "Top highlight", min: 0, max: 40, step: 1, unit: "%", def: 15 },
   { k: "--glass-scrim", label: "Under-text scrim", min: 0, max: 85, step: 1, unit: "%", def: 30 },
   { k: "--ambient", label: "Ambient intensity", min: 0, max: 2, step: 0.05, unit: "", def: 1.1 },
-  { k: "--bg-fade", label: "Backdrop fade", min: 40, max: 97, step: 1, unit: "%", def: 60 },
 ];
 
 const PALETTE: { k: string; label: string }[] = [

frontend/src/components/SettingsPanel.tsx

@@ -169,6 +169,24 @@ function Appearance({ prefs }: { prefs: PrefsController }) {
             onChange={(v) => setTheme({ ...theme, bgImage: v })}
           />
         </SettingRow>
+        {theme.mode === "dark" && theme.bgImage && (
+          <div className="pl-1 pb-1">
+            <div className="flex items-center justify-between text-xs text-muted mb-1">
+              <span>{t("settings.appearance.backgroundFade")}</span>
+              <span className="tabular-nums">{theme.bgFade}%</span>
+            </div>
+            <input
+              type="range"
+              min={0}
+              max={100}
+              step={1}
+              value={theme.bgFade}
+              onChange={(e) => setTheme({ ...theme, bgFade: Number(e.target.value) })}
+              aria-label={t("settings.appearance.backgroundFade")}
+              className="w-full accent-accent"
+            />
+          </div>
+        )}
         <SettingRow label={t("settings.appearance.listView")} hint={t("settings.appearance.listViewHint")}>
           <Switch
             label={t("settings.appearance.listView")}

frontend/src/i18n/locales/de/settings.json

@@ -35,6 +35,7 @@
     "darkMode": "Dunkler Modus",
     "backgroundImage": "Hintergrundbild",
     "backgroundImageHint": "Zeigt ein dezentes, themenbezogenes Hintergrundbild hinter der App, damit die Glasflächen etwas zum Brechen haben. Nur im dunklen Design; aus = einfarbig.",
+    "backgroundFade": "Bildabblendung",
     "listView": "Listenansicht",
     "listViewHint": "Zeigt den Feed als kompakte Liste statt als Kartenraster an.",
     "performanceMode": "Leistungsmodus",

frontend/src/i18n/locales/en/settings.json

@@ -35,6 +35,7 @@
     "darkMode": "Dark mode",
     "backgroundImage": "Background image",
     "backgroundImageHint": "Show a subtle per-theme backdrop image behind the app so the glass surfaces have something to refract. Dark theme only; off = flat colour.",
+    "backgroundFade": "Image fade",
     "listView": "List view",
     "listViewHint": "Show the feed as a compact list instead of a grid of cards.",
     "performanceMode": "Performance mode",

frontend/src/i18n/locales/hu/settings.json

@@ -35,6 +35,7 @@
     "darkMode": "Sötét mód",
     "backgroundImage": "Háttérkép",
     "backgroundImageHint": "Halvány, témánkénti háttérkép az app mögött, hogy az üveges felületeknek legyen mit megtörniük. Csak sötét témában; kikapcsolva sima szín.",
+    "backgroundFade": "Kép elhalványítása",
     "listView": "Listanézet",
     "listViewHint": "A hírfolyam kompakt listaként jelenik meg a kártyarács helyett.",
     "performanceMode": "Teljesítmény mód",

frontend/src/lib/theme.ts

@@ -18,6 +18,8 @@ export interface ThemePrefs {
   fontScale: number;
   /** Show the per-scheme background image (dark theme only); off = flat colour. */
   bgImage: boolean;
+  /** How strongly the background image is faded out, 0–100% (higher = fainter). */
+  bgFade: number;
 }
 
 export const DEFAULT_THEME: ThemePrefs = {
@@ -25,6 +27,7 @@ export const DEFAULT_THEME: ThemePrefs = {
   scheme: "midnight",
   fontScale: 1.06,
   bgImage: true,
+  bgFade: 60,
 };
 
 export function applyTheme(t: ThemePrefs): void {
@@ -32,6 +35,7 @@ export function applyTheme(t: ThemePrefs): void {
   el.dataset.theme = t.mode;
   el.dataset.scheme = t.scheme;
   el.style.setProperty("--font-scale", String(t.fontScale));
+  if (typeof t.bgFade === "number") el.style.setProperty("--bg-fade", `${t.bgFade}%`);
 }
 
 export function loadLocalTheme(): ThemePrefs {