Add weather simulation + debug-panel weather controls

- weatherSim config flag (default false): cycles through
  ['sunny','cloudy','stormy','night'] every weatherSimInterval ms
  instead of pulling open-meteo
- Debug-panel buttons: Sunny / Cloudy / Stormy / Night for
  instant manual switch; Auto-Cycle toggle, Stop, 5s/15s cycle
- Cleanup: removed duplicate unwrapped tick() in the init block
  (the wrapped one already starts the rAF chain)

The sim keeps the existing 5-minute palette transition between
states, so you still see the colour shift rather than a hard cut.

background.html

@@ -107,6 +107,22 @@
             border: 1px solid var(--stone);
             border-radius: 2px;
         }
+        .debug-row-buttons {
+            flex-wrap: wrap;
+            gap: 4px;
+        }
+        .dbg-btn {
+            background: var(--panel);
+            color: var(--icon);
+            border: 1px solid var(--border);
+            border-radius: 2px;
+            padding: 2px 8px;
+            font-size: 11px;
+            font-family: inherit;
+            cursor: pointer;
+        }
+        .dbg-btn:hover { background: var(--raised); }
+        .dbg-btn.dbg-btn-toggle.on { background: var(--ember); color: var(--dark); }
         .theme-table {
             font-size: 0.9em;
             margin-top: 4px;
@@ -339,7 +355,23 @@
             </div>
             <div class="debug-row"><span class="debug-label">Time:</span> <span id="dbg-time">--</span></div>
             <div class="debug-row"><span class="debug-label">Day%:</span> <span id="dbg-day">--</span></div>
-            <div class="debug-row"><span class="debug-label">Weather:</span> <span id="dbg-weather">--</span></div>
+            <div class="debug-row">
+                <span class="debug-label">Weather:</span>
+                <span id="dbg-weather">--</span>
+            </div>
+            <div class="debug-row debug-row-buttons">
+                <button class="dbg-btn" onclick="setWeatherTheme('sunny')">Sunny</button>
+                <button class="dbg-btn" onclick="setWeatherTheme('cloudy')">Cloudy</button>
+                <button class="dbg-btn" onclick="setWeatherTheme('stormy')">Stormy</button>
+                <button class="dbg-btn" onclick="setWeatherTheme('night')">Night</button>
+            </div>
+            <div class="debug-row debug-row-buttons">
+                <button class="dbg-btn dbg-btn-toggle" id="dbg-btn-sim"
+                        onclick="toggleWeatherSim()">Auto-Cycle: off</button>
+                <button class="dbg-btn" onclick="stopWeatherSim()">Stop</button>
+                <button class="dbg-btn" onclick="startWeatherSim(15000)">15s cycle</button>
+                <button class="dbg-btn" onclick="startWeatherSim(5000)">5s cycle</button>
+            </div>
             <div class="debug-row"><span class="debug-label">Theme:</span> <span id="dbg-theme">--</span></div>
             <div class="debug-row"><span class="debug-label">Speed:</span> <span id="dbg-speed">--</span></div>
             <div class="debug-row"><span class="debug-label">Transition:</span> <span id="dbg-trans">--</span></div>
@@ -1414,6 +1446,57 @@ window.weatherThemes = {
             }
         }
 
+        // ---- Weather simulation -----------------------------------------
+        // Cycles through a list of weather states automatically. Useful
+        // for A/B testing the renderer against every theme without
+        // waiting on the open-meteo API.
+        var simWeathers = ['sunny', 'cloudy', 'stormy', 'night'];
+        var simIndex = 0;
+        var simTimer = null;
+        var __weatherSimActive = false;
+
+        function startWeatherSim(intervalMs) {
+            stopWeatherSim();
+            var step = intervalMs || (window.CONFIG && window.CONFIG.weatherSimInterval) || 30000;
+            simIndex = 0;
+            setWeatherTheme(simWeathers[simIndex]);
+            simTimer = setInterval(function() {
+                simIndex = (simIndex + 1) % simWeathers.length;
+                setWeatherTheme(simWeathers[simIndex]);
+            }, step);
+            __weatherSimActive = true;
+        }
+
+        function stopWeatherSim() {
+            if (simTimer) {
+                clearInterval(simTimer);
+                simTimer = null;
+            }
+            __weatherSimActive = false;
+            updateSimButton();
+        }
+
+        function updateSimButton() {
+            var btn = document.getElementById('dbg-btn-sim');
+            if (btn) {
+                btn.textContent = 'Auto-Cycle: ' + (__weatherSimActive ? 'on' : 'off');
+                btn.classList.toggle('on', __weatherSimActive);
+            }
+        }
+
+        function toggleWeatherSim() {
+            if (__weatherSimActive) {
+                stopWeatherSim();
+            } else {
+                startWeatherSim();
+            }
+            updateSimButton();
+        }
+
+        // Periodically refresh the toggle state in case another tab
+        // toggled it.
+        setInterval(updateSimButton, 1000);
+
         function getEffectiveThemeColors() {
             if (!targetThemeColors) return null;
 
@@ -1983,9 +2066,14 @@ window.weatherThemes = {
         animate();
         try { tick(); } catch (e) { console.error('Initial tick error:', e); }
 
-        fetchWeather();
+        // Weather source: real open-meteo API or local simulation
-        setInterval(fetchWeather, 15 * 60 * 1000);
+        if (window.CONFIG && window.CONFIG.weatherSim) {
-        tick();
+            startWeatherSim(window.CONFIG.weatherSimInterval);
+            updateSimButton();
+        } else {
+            fetchWeather();
+            setInterval(fetchWeather, 15 * 60 * 1000);
+        }
     } catch (e) {
     window.__clouds2dError = e.message || String(e);
     console.error('Background init error:', e);

config.js

@@ -94,4 +94,12 @@ window.THEMES = {
     'ash': 'ash.css',
     'gruvbox': 'gruvbox.css',
     'nord': 'nord.css'
+
+    // weatherSim     - If true, ignore open-meteo and cycle through
+    //                   ['sunny', 'cloudy', 'stormy', 'night'] automatically
+    //                   every weatherSimInterval ms. Useful for testing
+    //                   every theme without waiting on the API.
+    // weatherSimInterval - Sim cycle period in ms (default 30000).
+    weatherSim: false,
+    weatherSimInterval: 30000,
 };