Add Picture screen: upload a file or point at a URL

New screen alongside clock/weather/navidrome. Upload goes through the web
UI (validated with PIL before accepting, stored under web/static/uploads/,
gitignored), or point it at a URL re-fetched every 30 minutes. Cover/contain
fit modes (new fit_cover/fit_contain helpers in render_utils.py, generalized
from the square-only cover-art cropping already used by the Navidrome
screen), plus the same contrast-boost/grayscale options that screen has.

web/app.py

@@ -2,10 +2,17 @@
 
 import requests
 from flask import Flask, redirect, render_template, request, url_for
+from PIL import Image
+from werkzeug.utils import secure_filename
+
+from screens.picture import UPLOAD_DIR
+
+ALLOWED_IMAGE_EXTENSIONS = {"png", "jpg", "jpeg", "gif", "bmp", "webp"}
 
 
 def create_app(config, screens: dict, scheduler) -> Flask:
     app = Flask(__name__)
+    app.config["MAX_CONTENT_LENGTH"] = 20 * 1024 * 1024  # 20 MB, generous for a photo
 
     @app.route("/")
     def index():
@@ -78,6 +85,54 @@ def create_app(config, screens: dict, scheduler) -> Flask:
 
         return render_template("settings_weather.html", settings=config.get_screen_settings("weather"), error=error)
 
+    @app.route("/settings/picture", methods=["GET", "POST"])
+    def settings_picture():
+        error = None
+        if request.method == "POST":
+            url = request.form.get("image_url", "").strip()
+            common_updates = {
+                "fit": request.form.get("fit", "cover"),
+                "boost_contrast": "boost_contrast" in request.form,
+                "grayscale": "grayscale" in request.form,
+            }
+            uploaded = request.files.get("image")
+
+            if uploaded and uploaded.filename:
+                filename = secure_filename(uploaded.filename)
+                ext = filename.rsplit(".", 1)[-1].lower() if "." in filename else ""
+                if ext not in ALLOWED_IMAGE_EXTENSIONS:
+                    error = "Unsupported file type -- use PNG, JPG, GIF, BMP, or WebP."
+                else:
+                    UPLOAD_DIR.mkdir(parents=True, exist_ok=True)
+                    # Only one picture is ever active -- clear any previous
+                    # upload first so a different extension doesn't leave an
+                    # orphaned file behind.
+                    for old in UPLOAD_DIR.glob("current.*"):
+                        old.unlink()
+                    dest = UPLOAD_DIR / f"current.{ext}"
+                    uploaded.save(dest)
+                    try:
+                        Image.open(dest).verify()
+                    except Exception:
+                        dest.unlink(missing_ok=True)
+                        error = "That file doesn't look like a valid image."
+                    else:
+                        config.update_screen_settings("picture", {
+                            "mode": "upload",
+                            "uploaded_filename": dest.name,
+                            **common_updates,
+                        })
+                        return redirect(url_for("settings_picture", saved=1))
+            elif url:
+                config.update_screen_settings("picture", {"mode": "url", "image_url": url, **common_updates})
+                return redirect(url_for("settings_picture", saved=1))
+            else:
+                # Neither a new upload nor a URL change -- just update fit/boost/grayscale.
+                config.update_screen_settings("picture", common_updates)
+                return redirect(url_for("settings_picture", saved=1))
+
+        return render_template("settings_picture.html", settings=config.get_screen_settings("picture"), error=error)
+
     @app.route("/settings/rotation", methods=["GET", "POST"])
     def settings_rotation():
         if request.method == "POST":