feat: implement probe renaming and settings management via API

frontend/templates/index.html

@@ -28,7 +28,12 @@
           <textarea id="session-notes" placeholder="Notes (freeform)"></textarea>
           <button type="submit">Start New Session</button>
         </form>
-        <button id="end-session-btn" disabled>End Session</button>
+        <button id="end-session-btn" disabled>End Active Session</button>
+      </div>
+
+      <div class="panel">
+        <h2>Past Sessions</h2>
+        <div id="past-sessions"><p class="muted">Loading…</p></div>
       </div>
     </section>
 
@@ -38,7 +43,7 @@
 
     <section id="charts">
       <div class="panel">
-        <h2>Temperature History</h2>
+        <h2>Temperature History <span id="chart-session-label" class="muted"></span></h2>
         <div class="chart-controls">
           <label>Range:
             <select id="chart-range">
@@ -50,7 +55,9 @@
           </label>
           <button id="refresh-chart-btn">Refresh Chart</button>
         </div>
-        <canvas id="temp-chart"></canvas>
+        <div class="chart-container">
+          <canvas id="temp-chart"></canvas>
+        </div>
       </div>
     </section>
   </main>