feat: Bing wallpaper slideshow — 12 images, hourly rotation, weekly cleanup

- Frontend: fullscreen wallpaper background with 1.5s crossfade transition,
  login card centered with glass effect, images rotate every hour
- Backend: new /api/settings/bing-wallpapers endpoint fetches 8 recent images
  from Bing HPImageArchive, caches to web/app/wallpapers/, returns all URLs
- Auto-cleanup: removes files older than 7 days, keeps max 12 newest
- Old /bing-wallpaper endpoint kept for backward compatibility

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/api/settings.py

@@ -1264,31 +1264,109 @@ def _retry_to_dict(job: PushRetryJob) -> dict:
     }
 
 
-# ── Bing Daily Wallpaper — download + cache to disk ──
+# ── Bing Daily Wallpaper — download 12+ images, rotate hourly ──
 _WALLPAPER_DIR = Path(__file__).resolve().parent.parent.parent / "web" / "app" / "wallpapers"
+_MAX_WALLPAPERS = 12  # keep 12 images (12 hours rotation before repeat)
+_MAX_AGE_DAYS = 7     # auto-clean older than 7 days
 
-@router.get("/bing-wallpaper", response_model=dict)
-async def bing_wallpaper():
-    """Download the Bing daily wallpaper, cache to disk, return the local URL.
 
-    No auth required — used by the login page.
-    A cron job or this endpoint itself cleans up wallpapers older than 7 days.
+def _cleanup_old_wallpapers() -> int:
+    """Remove wallpapers older than 7 days. Returns count removed."""
+    import time
+    from datetime import datetime, timedelta
+    cutoff = datetime.utcnow() - timedelta(days=_MAX_AGE_DAYS)
+    removed = 0
+    for f in sorted(_WALLPAPER_DIR.glob("*.jpg")):
+        try:
+            mtime = datetime.utcfromtimestamp(f.stat().st_mtime)
+            if mtime < cutoff:
+                f.unlink()
+                removed += 1
+        except Exception:
+            pass
+    return removed
+
+
+@router.get("/bing-wallpapers", response_model=dict)
+async def bing_wallpapers():
+    """Return all cached wallpaper URLs for frontend slideshow rotation.
+
+    Syncs with Bing daily (pulls up to 8 days of images), caches to disk,
+    cleans up old files, returns sorted list of local URLs.
     """
     import httpx
     from datetime import datetime, timedelta
 
     _WALLPAPER_DIR.mkdir(parents=True, exist_ok=True)
 
-    today = datetime.utcnow().strftime("%Y-%m-%d")
-    cached = _WALLPAPER_DIR / f"{today}.jpg"
-
-    # Return cached version if already downloaded today
-    if cached.exists() and cached.stat().st_size > 1024:
-        return {"url": f"/app/wallpapers/{today}.jpg"}
-
+    # Download today + last 7 days from Bing (n=8 gives ~8 images)
+    downloaded = 0
     try:
+        async with httpx.AsyncClient(timeout=12.0) as client:
+            # Fetch up to 8 recent images from Bing
+            resp = await client.get(
+                "https://cn.bing.com/HPImageArchive.aspx",
+                params={"format": "js", "idx": 0, "n": 8, "mkt": "zh-CN"},
+            )
+            data = resp.json()
+            for img in (data.get("images") or []):
+                img_path = img.get("url")
+                if not img_path:
+                    continue
+                # Use date from Bing metadata as filename
+                date_str = img.get("startdate", "") or img.get("fullstartdate", "")[:8] or ""
+                if not date_str:
+                    # fallback: extract from URL
+                    import re
+                    m = re.search(r'OHR\.(\w+)_', img_path)
+                    date_str = m.group(1) if m else f"unknown_{downloaded}"
+
+                cached = _WALLPAPER_DIR / f"{date_str}.jpg"
+                if cached.exists() and cached.stat().st_size > 1024:
+                    continue  # already cached
+
+                try:
+                    img_resp = await client.get(f"https://cn.bing.com{img_path}")
+                    if img_resp.status_code == 200:
+                        cached.write_bytes(img_resp.content)
+                        downloaded += 1
+                except Exception:
+                    continue
+    except Exception:
+        pass
+
+    # Cleanup old files
+    _cleanup_old_wallpapers()
+
+    # Also keep only newest N files if we somehow have too many
+    all_files = sorted(_WALLPAPER_DIR.glob("*.jpg"), key=lambda f: f.stat().st_mtime, reverse=True)
+    for f in all_files[_MAX_WALLPAPERS:]:
+        try:
+            f.unlink()
+        except Exception:
+            pass
+
+    # Return sorted URLs (newest first)
+    urls = [f"/app/wallpapers/{f.name}" for f in sorted(all_files[:_MAX_WALLPAPERS], key=lambda f: f.name, reverse=True)]
+    return {"urls": urls, "count": len(urls)}
+
+
+# Keep the old single-image endpoint for backward compatibility
+@router.get("/bing-wallpaper", response_model=dict)
+async def bing_wallpaper():
+    """Return today's wallpaper URL (backward compat)."""
+    try:
+        import httpx
+        from datetime import datetime
+
+        _WALLPAPER_DIR.mkdir(parents=True, exist_ok=True)
+        today = datetime.utcnow().strftime("%Y-%m-%d")
+        cached = _WALLPAPER_DIR / f"{today}.jpg"
+
+        if cached.exists() and cached.stat().st_size > 1024:
+            return {"url": f"/app/wallpapers/{today}.jpg"}
+
         async with httpx.AsyncClient(timeout=10.0) as client:
-            # 1. Get today's image metadata
             resp = await client.get(
                 "https://cn.bing.com/HPImageArchive.aspx",
                 params={"format": "js", "idx": 0, "n": 1, "mkt": "zh-CN"},
@@ -1297,32 +1375,17 @@ async def bing_wallpaper():
             img = (data.get("images") or [{}])[0]
             img_url = img.get("url")
             if not img_url:
-                raise ValueError("no image url from Bing")
+                return {"url": None}
 
-            # 2. Download the actual image
             img_resp = await client.get(f"https://cn.bing.com{img_url}")
-            if img_resp.status_code != 200:
-                raise ValueError(f"Bing returned {img_resp.status_code}")
-
-            # 3. Save to disk
-            cached.write_bytes(img_resp.content)
-
-            # 4. Remove wallpapers older than 7 days
-            cutoff = datetime.utcnow() - timedelta(days=7)
-            for f in _WALLPAPER_DIR.glob("*.jpg"):
-                try:
-                    mtime = datetime.utcfromtimestamp(f.stat().st_mtime)
-                    if mtime < cutoff:
-                        f.unlink()
-                except Exception:
-                    pass
+            if img_resp.status_code == 200:
+                cached.write_bytes(img_resp.content)
 
+            _cleanup_old_wallpapers()
+        return {"url": f"/app/wallpapers/{today}.jpg"}
     except Exception:
-        # If download fails, try yesterday's cached file
-        yesterday = (datetime.utcnow() - timedelta(days=1)).strftime("%Y-%m-%d")
-        yesterday_cached = _WALLPAPER_DIR / f"{yesterday}.jpg"
-        if yesterday_cached.exists():
-            return {"url": f"/app/wallpapers/{yesterday}.jpg"}
+        # Try any cached file
+        cached_list = sorted(_WALLPAPER_DIR.glob("*.jpg"))
+        if cached_list:
+            return {"url": f"/app/wallpapers/{cached_list[-1].name}"}
         return {"url": None}
-
-    return {"url": f"/app/wallpapers/{today}.jpg"}