fix: improve sensing accuracy, presence detection, and UI reliability

[KarthikV17]

Server-side fixes (sensing-server)

• Fix ADR-018 packet parsing: correct byte offsets for 20-byte header
  • n_subcarriers: u8 → u16 at bytes [6..7]
  • freq_mhz: u16 → u32 at bytes [8..11]
  • RSSI at byte 16, noise floor at byte 17
• Tune presence detection for faster response:
  • DEBOUNCE_FRAMES: 4 → 2 (faster state transitions)
  • MOTION_EMA_ALPHA: 0.15 → 0.25 (more responsive)
• Add asymmetric person count smoothing:
  • α=0.35 decay when someone leaves (~2-3s response)
  • α=0.20 rise when someone enters (~3-4s response)
  • Prevents false jumps while staying responsive

Firmware fixes (esp32-csi-node)

• Read node_id from NVS config instead of compile-time CONFIG_CSI_NODE_ID
  • Enables unique node IDs per device via provisioning
  • Updated: csi_collector.c, edge_processing.c, wasm_runtime.c, display_ui.c
• Add extern declaration for g_nvs_config in nvs_config.h
• Update provision.py to support both esp32s3 and esp32c6 chips

UI fixes (Observatory)

• Add WebSocket auto-reconnect with exponential backoff:
  • Retries up to 5 times (1s, 2s, 4s, 8s, 16s delays)
  • Shows "RECONNECTING" status with blue pulsing indicator
  • Only falls back to demo mode after all retries exhausted
• Prevents random switches from Live to Demo mode

Tools

• Add csi_inspector.py for packet debugging with correct ADR-018 offsets

[KarthikV17]

@ruvnet please review and let me know if there is any additional testing needed. This has been verified with ESP32-S3.