feat: ESP32 CSI MAC address filtering with NVS/Kconfig support (#101)

* feat: add MAC address filter for ESP32 CSI collection

In multi-AP environments, CSI frames from different access points get
mixed together, corrupting the sensing signal. Add transmitter MAC
filtering so only frames from a specified AP are processed.

Implementation:
- csi_collector: filter in wifi_csi_callback by comparing info->mac
  against configured MAC; log transmitter MAC in periodic debug output
- csi_collector_set_filter_mac(): runtime API to enable/disable filter
- Kconfig: CSI_FILTER_MAC option (format "AA:BB:CC:DD:EE:FF")
- NVS: "filter_mac" 6-byte blob overrides Kconfig at runtime
- nvs_config: parse Kconfig MAC string at boot, load NVS override
- main: apply filter from config after csi_collector_init()

When no filter is configured (default), behavior is unchanged —
all transmitter MACs are accepted for backward compatibility.

Fixes #98

Co-Authored-By: claude-flow <ruv@ruv.net>

* chore: add CLAUDE.local.md to .gitignore

Local machine configuration (ESP-IDF paths, COM port, build
instructions) should not be committed to the repository.

Co-Authored-By: claude-flow <ruv@ruv.net>

.gitignore

@@ -1,3 +1,6 @@
+# Local machine configuration (not shared)
+CLAUDE.local.md
+
 # ESP32 firmware build artifacts and local config (contains WiFi credentials)
 firmware/esp32-csi-node/build/
 firmware/esp32-csi-node/sdkconfig