feat(ec718): support binpkg flashing over USB and UART1

[aix402]

Adds EC718 .binpkg flashing support and UART1 download mode.

Highlights:

• Add flash run --binpkg for EC718 raw binpkg packages.
• Keep existing USB auto-enter boot behavior as the default path.
• Add explicit --port-mode auto|usb|uart.
• Add UART1 detect flow using AT+ECRST=delay,650 + 7E 00 02 7E and ec718m_uart.bin.
• Add --agent-baud / --agbaud for AgentBoot/download baud override; keep --force-br as hidden compatibility alias.
• Add --at-baud for UART1 AT reset baud override.
• Document EC718 USB/UART1 protocol details.

Validated locally on ML307N/EC718PM:

• cargo +stable-x86_64-pc-windows-gnu fmt -- --check
• cargo +stable-x86_64-pc-windows-gnu check -p luatos-cli -p luatos-flash -p luatos-mfgui
• cargo +stable-x86_64-pc-windows-gnu build -p luatos-cli
• USB auto flashing from runtime COM port to download COM port succeeded.
• UART1 flashing on COM6 succeeded at --agent-baud 460800.

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