fix: Remove non-functional Node Discovery feature

Removed Node Discovery feature that was experiencing persistent timeout
issues. Feature attempted to scan mesh network for nearby repeaters but
consistently failed due to bridge timing constraints.

Changes:
- Remove node_discover() function from cli.py
- Remove 'node_discover' from SPECIAL_COMMANDS in api.py
- Remove Discover Nodes button and modal from base.html
- Remove discoverNodes() and displayNodeDiscoveryResults() from app.js
- Remove Discover Nodes documentation from README.md

IMPORTANT: Advert message cleanup ("Advert sent") is preserved and
working correctly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

README.md

@@ -521,24 +521,6 @@ Sends a single advertisement frame to announce your node's presence in the mesh
 2. Click "Send Advert" under Network Commands
 3. Wait for confirmation toast
 
-#### Discover Nodes
-Scans the mesh network to find nearby repeaters and displays their signal quality. Useful for network diagnostics and finding the best repeater connections.
-
-1. Click the menu icon (☰) in the navbar
-2. Click "Discover Nodes" under Network Commands
-3. A modal window opens showing nearby repeaters with:
-   - **Node ID**: Public key prefix and tag
-   - **SNR (Signal-to-Noise Ratio)**: Higher is better (>10dB = excellent, 5-10dB = good, <5dB = poor)
-   - **RSSI**: Received signal strength in dBm
-   - **SNR In**: Inbound signal quality
-   - **Hops**: Number of hops to reach the node
-4. Click "Refresh" to rescan for nodes
-
-Results are sorted by signal strength (strongest first) and color-coded:
-- 🟢 **Green**: SNR ≥ 10dB (excellent connection)
-- 🟡 **Yellow**: SNR 5-10dB (good connection)
-- 🔴 **Red**: SNR < 5dB (poor connection)
-
 #### Flood Advert (Use Sparingly!)
 Sends advertisement in flooding mode, forcing all nodes to retransmit. **Use only when:**
 - Starting a completely new network