feat: add active time window to countdown rules

UI: Active Window Start/End time inputs on countdown form.
Leave blank = runs any time. End before start = crosses midnight.
Scheduler: checks current time against window before starting timer;
supports cross-midnight windows (e.g. 9:00 AM to 4:00 AM next day).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/homebridge-plugin/homebridge-ui/public/index.html

@@ -394,10 +394,6 @@
       </div>
 
       <div id="dwm-countdown-fields" style="display:none">
-        <div class="form-group">
-          <label>Countdown Duration (minutes)</label>
-          <input type="number" id="dwm-countdown-mins" min="1" max="1440" placeholder="60" />
-        </div>
         <div class="form-group">
           <label>Condition</label>
           <select id="dwm-countdown-action">
@@ -405,6 +401,22 @@
             <option value="off_to_on">If device turns OFF → auto-ON after duration</option>
           </select>
         </div>
+        <div class="form-group">
+          <label>Countdown Duration (minutes)</label>
+          <input type="number" id="dwm-countdown-mins" min="1" max="1440" placeholder="60" />
+        </div>
+        <div class="flex-row">
+          <div class="form-group" style="flex:1">
+            <label>Active Window Start</label>
+            <input type="text" id="dwm-countdown-window-start" placeholder="e.g. 9:00 AM" />
+          </div>
+          <div class="form-group" style="flex:1">
+            <label>Active Window End</label>
+            <input type="text" id="dwm-countdown-window-end" placeholder="e.g. 4:00 AM" />
+            <div style="font-size:0.75rem;color:var(--muted);margin-top:3px">End before start = next day</div>
+          </div>
+        </div>
+        <div style="font-size:0.75rem;color:var(--muted);margin-bottom:8px">Leave window blank to run at any time.</div>
       </div>
 
       <div id="dwm-alwayson-info" style="display:none;margin-bottom:12px;padding:10px;background:rgba(48,209,88,.1);border:1px solid rgba(48,209,88,.3);border-radius:6px;font-size:0.82rem;color:#4ade80">