Remove thermostat/indoor sensor integration

Ecobee API is closed to new developer registrations and iOS sub-daily
automations are no longer available, making the HomeKit push approach
unworkable. Removes all related code:

- server.js: HomeKit push endpoints, token management, data files
- dashboard.html: thermostat section card, indoor stat tiles, indoor
  charts, HomeKit settings panel, HVAC badge CSS, all related JS
- index.html: Indoor Temp stat card
- app.js: indoor sensor display logic

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

app/public/index.html

@@ -289,11 +289,6 @@
                 <div class="stat-label">Solar Rad.</div>
                 <div class="stat-val"><span id="st-solar">--</span> <span class="stat-unit">W/m²</span></div>
               </div>
-              <div class="stat-card" id="st-indoor-card" class="hidden">
-                <div class="stat-label">Indoor Temp</div>
-                <div class="stat-val"><span id="st-tempin">--</span>°</div>
-                <div class="stat-sub" id="st-humin"></div>
-              </div>
             </div>
           </div>
           <div id="station-error" class="station-error hidden"></div>