feat: add OOK/AM envelope detection mode to Morse decoder

Re-implements envelope detection on top of the rewritten Morse decoder.
Addresses PR #160 review feedback:
- Rebase: rebuilt on current upstream/main (lifecycle state machine)
- Gap thresholds: 2.0/5.0 for envelope only; goertzel keeps 2.6/6.0
- Frequency validation: max_mhz=1766 for envelope, 30 for goertzel
- Tests: EnvelopeDetector unit tests + envelope-mode decoder test
- Envelope uses direct magnitude threshold (no SNR/noise ref)
- Goertzel path completely unchanged

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

templates/partials/modes/morse.html

@@ -3,21 +3,39 @@
     <div class="section">
         <h3>CW/Morse Decoder</h3>
         <p class="info-text morse-mode-help">
-            Decode CW (continuous wave) Morse with USB demod + Goertzel tone detection.
-            Start with 700 Hz tone and 200 Hz bandwidth.
+            Decode CW (continuous wave) Morse code. Supports HF amateur bands (USB + Goertzel tone
+            detection) and ISM/UHF OOK signals (AM + envelope detection).
         </p>
     </div>
 
+    <div class="section">
+        <h3>Detection Mode</h3>
+        <div class="form-group">
+            <div style="display: flex; gap: 4px;">
+                <button class="preset-btn morseDetectBtn" id="morseDetectGoertzel"
+                        onclick="MorseMode.setDetectMode('goertzel')"
+                        style="flex: 1; background: var(--accent); color: #000;">CW Tone</button>
+                <button class="preset-btn morseDetectBtn" id="morseDetectEnvelope"
+                        onclick="MorseMode.setDetectMode('envelope')"
+                        style="flex: 1;">OOK Envelope</button>
+            </div>
+            <input type="hidden" id="morseDetectMode" value="goertzel">
+            <p id="morseDetectHint" class="info-text" style="font-size: 10px; color: var(--text-dim); margin-top: 4px;">
+                CW Tone: HF bands, USB demod, Goertzel filter. For amateur CW.
+            </p>
+        </div>
+    </div>
+
     <div class="section">
         <h3>Frequency</h3>
         <div class="form-group">
             <label>Frequency (MHz)</label>
-            <input type="number" id="morseFrequency" value="14.060" step="0.001" min="0.5" max="30" placeholder="e.g., 14.060">
+            <input type="number" id="morseFrequency" value="14.060" step="0.001" min="0.5" max="1766" placeholder="e.g., 14.060">
             <span class="help-text morse-help-text">Enter CW center frequency in MHz (e.g., 7.030 for 40m).</span>
         </div>
         <div class="form-group">
             <label>Band Presets</label>
-            <div class="morse-presets">
+            <div class="morse-presets" id="morseHFPresets">
                 <button class="preset-btn" onclick="MorseMode.setFreq(3.560)">80m</button>
                 <button class="preset-btn" onclick="MorseMode.setFreq(7.030)">40m</button>
                 <button class="preset-btn" onclick="MorseMode.setFreq(10.116)">30m</button>
@@ -27,6 +45,13 @@
                 <button class="preset-btn" onclick="MorseMode.setFreq(24.910)">12m</button>
                 <button class="preset-btn" onclick="MorseMode.setFreq(28.060)">10m</button>
             </div>
+            <div class="morse-presets" id="morseISMPresets" style="display: none; flex-wrap: wrap; gap: 4px;">
+                <button class="preset-btn" onclick="MorseMode.setFreq(315.000)">315</button>
+                <button class="preset-btn" onclick="MorseMode.setFreq(433.300)">433.3</button>
+                <button class="preset-btn" onclick="MorseMode.setFreq(433.920)">433.9</button>
+                <button class="preset-btn" onclick="MorseMode.setFreq(868.000)">868</button>
+                <button class="preset-btn" onclick="MorseMode.setFreq(915.000)">915</button>
+            </div>
         </div>
     </div>
 
@@ -42,7 +67,7 @@
         </div>
     </div>
 
-    <div class="section">
+    <div class="section" id="morseToneFreqGroup">
         <h3>CW Detector</h3>
         <div class="form-group">
             <label>Tone Frequency: <span id="morseToneFreqLabel">700</span> Hz</label>
@@ -154,12 +179,18 @@
         </div>
     </div>
 
-    <div class="section">
+    <div class="section" id="morseHFNote">
         <p class="info-text morse-hf-note">
             CW on HF (1-30 MHz) requires an HF-capable SDR path (direct sampling or upconverter)
             and an appropriate antenna.
         </p>
     </div>
+    <div class="section" id="morseEnvelopeNote" style="display: none;">
+        <p class="info-text" style="font-size: 11px; color: #ffaa00; line-height: 1.5;">
+            OOK Envelope mode uses AM demodulation to detect carrier on/off keying.
+            Suitable for ISM-band (315/433/868/915 MHz) Morse transmitters.
+        </p>
+    </div>
 
     <button class="run-btn" id="morseStartBtn" onclick="MorseMode.start()">Start Decoder</button>
     <button class="stop-btn" id="morseStopBtn" onclick="MorseMode.stop()" style="display: none;">Stop Decoder</button>