feat: ESP32-C5 hardware target for dual-band (2.4 + 5 GHz) WiFi scanning

[dougborg]

Summary

The ESP32-C5 is Espressif's first chip with native 5GHz WiFi support. Many surveillance devices (Flock Safety, some Ring cameras, corporate tracking APs) operate on 5GHz bands. AirHound currently only scans 2.4GHz channels 1–13, missing a significant portion of the wireless landscape.

Inspired by ESP32DualBandWardriver, which ships on the ESP32-C5-DevKitC-1 v1.2.

Key Points

• ESP32-C5-DevKitC-1 v1.2 is available now
• esp-hal C5 support is maturing — RISC-V architecture (not Xtensa), simpler toolchain
• Promiscuous mode on C5 covers both 2.4GHz and 5GHz bands natively
• Channel list expands from 13 to 13 + ~25 5GHz channels (36–165)
• scanner.rs frame parsing is band-agnostic (802.11 is 802.11) — no changes needed
• board.rs needs a new board variant with C5 pin definitions
• Build system needs a third Docker target (esp32c5)

Implementation Considerations

• Channel hopping strategy (lib: channel strategy module (channel.rs) #30) needs a 5GHz channel plan — dwell time allocation across ~38 channels matters more than with 13
• May want configurable band selection (2.4 only, 5 only, both) in FilterConfig
• C5 is RISC-V, so no Xtensa toolchain needed — could simplify CI

Relates To

• arch: multi-platform architecture — shared core, multiple runtimes #17 — multi-platform architecture
• arch: evaluate ESP-IDF (std) migration for ESP32 firmware #18 — ESP-IDF evaluation
• lib: channel strategy module (channel.rs) #30 — channel scheduling and dwell optimization