feat(scale): add manual USB-powered override for Skale

[MaxRink]

Summary

Add a default-off “Powered by USB” declaration for each native Skale. Persist enabled device IDs, apply settings independently, suppress battery reads while enabled, and refresh battery metadata when disabled.

Linked Issue

Fixes #716

Verification

• Combined Linux Flutter gate for the current publication stack: 4,315 passed, 1 skipped, 0 failed; analyzer clean (48.0s). Source was unchanged during the gate.

• Combined simulated runtime checks passed for the current stack; no production fixes were needed during runtime validation.

Impact

The manual declaration is stored in skalePoweredByUsbByDevice, including REST settings and export/import. Only enabled IDs are stored. It does not detect electrical power. Connected metadata uses the narrow DeviceInformationCapable capability; /api/v1/scale/info remains limited to firmware and optional battery, and device inventory REST/WS contracts remain unchanged. Low-battery warning policy remains in #717. This branch includes the firmware and battery foundations from #742 and #743. API and device documentation are updated.

Contributor Responsibility

AI-assisted development is allowed. The submitter remains responsible for the submitted work.

• I have reviewed and understand all changes in this PR and take responsibility for their correctness, security, behavior, licensing, and provenance, including any AI-assisted or AI-generated work.

[tadelv]

Please remove the orphan DeviceInformation components from both REST and WebSocket specs here as well. This branch currently extends those unused schemas with powerSource / powerSourceProvenance, which makes the public specs imply a metadata API that the corrected architecture explicitly does not provide. The PR body now says /api/v1/scale/info stays limited to firmware/battery and USB is a manual per-device setting; the specs should match that boundary. Keep the internal DeviceInformation fields for the native Devices UI if needed, and expose the manual override through the settings contract only.

[MaxRink]

Addressed the orphan-schema review in 4c103e0: removed DeviceInformation from both REST and WebSocket components, including the unused powerSource/powerSourceProvenance properties. ScaleInfo, internal native-UI metadata, and the manual USB override settings remain unchanged.