feat(backlight): support HID++ 0x1982

[kirgene]

The MX Keys backlight is HID++ 0x1982. The wrapper for it already exists in openlogi-hidpp but nothing calls it, BacklightFeature only shows up in the feature registry. Capabilities::lighting tracks 0x8070/0x8080 and stays false for these keyboards, and diag lighting drives only those two, so there's no path to the backlight on an MX Keys S.

This wires it up: openlogi-hid::backlight for the IPC-facing types (same shape as smartshift), openlogi-hid::write::backlight with route-based get_backlight and set_backlight_enabled, and an openlogi backlight [status|off|on] command.

set_backlight_enabled reads getBacklightConfig first and writes everything except the enable bit back unchanged, so mode, effect, level and the three fade-out durations survive a toggle. The effect goes out as the 0xff "do not change" sentinel. TemporaryManual maps to Automatic on the way back down since setBacklightConfig can't write it.

I put the command at top level rather than under diag because setBacklightConfig writes to NVM, and diag.rs describes itself as diagnosis that doesn't touch persistent state. Can move it if you'd rather.

The two new HidppOperation variants are appended, so bincode variant indices don't shift and the wire_format goldens still pass.

Tested on an MX Keys S behind a Bolt receiver:

$ openlogi backlight
device: MX KEYS S (slot 1 on receiver ...)
  current: enabled=true mode=automatic (ambient-light sensor) status=on (following ambient light) level=2/8

$ openlogi backlight off
device: MX KEYS S (slot 1 on receiver ...)
  current: enabled=true mode=automatic (ambient-light sensor) status=on (following ambient light) level=2/8
  read-back: enabled=false mode=automatic (ambient-light sensor) status=off (disabled by software) level=0/8

Unit tests cover the enum mapping and the CLI parsing.

No GUI changes. The panel would need a different shape than the RGB colour picker, so that seemed like a separate PR.

[greptile-apps]

Greptile Summary

This PR adds persistent HID++ 0x1982 keyboard-backlight control.

• Adds route-based backlight state reads and enable/disable writes while preserving writable configuration fields.
• Adds IPC-facing backlight state, mode, and status types.
• Adds the top-level openlogi backlight [status|off|on] command and parsing tests.

Confidence Score: 4/5

The PR should not merge until the temporary-manual conversion notice is tied to the state actually consumed by the write.

A keyboard-key adjustment between the CLI pre-read and the setter's independent configuration read can make the setter convert TemporaryManual to Automatic without displaying the intended warning.

Files Needing Attention: crates/openlogi-cli/src/cmd/backlight.rs and crates/openlogi-hid/src/write/backlight.rs

Important Files Changed

Filename	Overview
crates/openlogi-cli/src/cmd/backlight.rs	Adds the command and user-facing state output, but its temporary-mode warning can be invalidated by the setter's later live read.
crates/openlogi-hid/src/write/backlight.rs	Implements the 0x1982 read-modify-write path and explicitly maps the firmware-only temporary mode to automatic.
crates/openlogi-hid/src/backlight.rs	Adds serialized backlight state, mode, and status domain types.
crates/openlogi-hid/src/write/error.rs	Appends backlight operation identifiers without shifting existing serialized enum indices.

Sequence Diagram

sequenceDiagram
  participant User
  participant CLI as openlogi backlight
  participant HID as openlogi-hid
  participant Keyboard
  CLI->>HID: get_backlight(route)
  HID->>Keyboard: getBacklightConfig + getBacklightInfo
  Keyboard-->>CLI: current state
  User->>Keyboard: optional backlight-key adjustment
  CLI->>HID: set_backlight_enabled(route, enabled)
  HID->>Keyboard: getBacklightConfig
  HID->>Keyboard: setBacklightConfig
  HID->>Keyboard: read-back
  Keyboard-->>CLI: resulting state

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