feat: WiFi Locate mode, mobile nav groups, v2.24.0

Add WiFi Locate mode for locating access points by BSSID with real-time
signal meter, distance estimation, RSSI history chart, and audio
proximity tones. Includes hand-off from WiFi detail drawer, environment
presets (Free Space/Outdoor/Indoor), and signal-lost detection.

Also includes:
- Mobile navigation reorganized into labeled groups (SIG/TRK/SPC/WIFI/INTEL/SYS)
- flask-limiter made optional with graceful degradation
- Fix radiosonde setup missing semver Python dependency
- Documentation updates (FEATURES, USAGE, UI_GUIDE, GitHub Pages site)

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

templates/partials/modes/wifi_locate.html

@@ -0,0 +1,66 @@
+<!-- WIFI LOCATE MODE -->
+<div id="wflMode" class="mode-content">
+    <div class="section">
+        <h3>WiFi Locate</h3>
+        <p class="info-text" style="font-size: 11px; color: var(--text-dim); margin-bottom: 12px;">
+            Locate a WiFi access point by BSSID &mdash; real-time signal strength meter with proximity audio.
+        </p>
+    </div>
+
+    <!-- Target Lock -->
+    <div class="section">
+        <h3>Target</h3>
+        <div id="wflHandoffCard" style="display: none; background: rgba(0,255,136,0.08); border: 1px solid rgba(0,255,136,0.3); border-radius: 6px; padding: 8px; margin-bottom: 8px;">
+            <div style="display: flex; justify-content: space-between; align-items: center;">
+                <span style="font-size: 10px; color: var(--accent-green); text-transform: uppercase; font-weight: 600;">Handed off from WiFi</span>
+                <button onclick="WiFiLocate.clearHandoff()" style="background: none; border: none; color: var(--text-dim); cursor: pointer; font-size: 10px;">&times;</button>
+            </div>
+            <div id="wflHandoffName" style="font-size: 12px; font-weight: 600; color: var(--text-primary); margin-top: 4px;"></div>
+            <div id="wflHandoffMeta" style="font-size: 10px; color: var(--text-dim); font-family: var(--font-mono);"></div>
+        </div>
+
+        <label class="input-label">BSSID (MAC Address)</label>
+        <input type="text" id="wflBssid" class="text-input" placeholder="AA:BB:CC:DD:EE:FF" style="font-family: var(--font-mono); font-size: 11px;">
+    </div>
+
+    <!-- Environment Preset -->
+    <div class="section">
+        <h3>Environment</h3>
+        <div class="wfl-env-grid">
+            <button class="wfl-env-btn" data-env="FREE_SPACE" onclick="WiFiLocate.setEnvironment('FREE_SPACE')">
+                <span class="wfl-env-icon">&#127968;</span>
+                <span class="wfl-env-label">Open Field</span>
+                <span class="wfl-env-n">n=2.0</span>
+            </button>
+            <button class="wfl-env-btn active" data-env="OUTDOOR" onclick="WiFiLocate.setEnvironment('OUTDOOR')">
+                <span class="wfl-env-icon">&#127795;</span>
+                <span class="wfl-env-label">Outdoor</span>
+                <span class="wfl-env-n">n=2.8</span>
+            </button>
+            <button class="wfl-env-btn" data-env="INDOOR" onclick="WiFiLocate.setEnvironment('INDOOR')">
+                <span class="wfl-env-icon">&#127970;</span>
+                <span class="wfl-env-label">Indoor</span>
+                <span class="wfl-env-n">n=3.5</span>
+            </button>
+        </div>
+    </div>
+
+    <!-- Info note -->
+    <div class="section">
+        <p class="info-text" style="font-size: 10px; color: var(--text-dim);">
+            Deep scan recommended for continuous RSSI tracking. Will auto-start if not running.
+        </p>
+    </div>
+
+    <!-- Controls -->
+    <div class="section">
+        <div style="display: flex; gap: 6px;">
+            <button class="run-btn" id="wflStartBtn" onclick="WiFiLocate.start()">Start Locate</button>
+            <button class="stop-btn" id="wflStopBtn" onclick="WiFiLocate.stop()" style="display: none;">Stop</button>
+        </div>
+        <div id="wflScanStatus" style="display: none; margin-top: 6px; font-size: 10px; color: var(--text-dim);">
+            <span id="wflScanDot" style="display: inline-block; width: 6px; height: 6px; border-radius: 50%; background: #22c55e; margin-right: 4px; vertical-align: middle;"></span>
+            <span id="wflScanText">WiFi scanner active</span>
+        </div>
+    </div>
+</div>