TOML file upload in /manage

[SIR-R0B]

FEATURE — TOML file upload in /manage

Add an "Upload" button next to the existing Copy/Download/Refresh buttons in the Raw Config section.

This needs:

A new POST /manage/config/upload endpoint in the Rust server that accepts a TOML body, validates it (at minimum: check for duplicate section headers, check that [channels_config] and [autonomy] exist), writes to OPENCLAW_CONFIG, chmods 600, and restarts the agent.
A file input + JS handler in the UI that reads the file as text and POSTs it.
A confirmation dialog: "This will replace the entire agent config and restart the agent. Continue?"
The endpoint should snapshot the config before and after so the diff viewer works.

HTML addition to the cfg-actions div:
htmlUpload