Rename `eyeDropper.sRGBHex()` to `.value()`

[vs-borodin]

Which @signality/* package(s) are relevant/related to the feature request?

core

Description

EyeDropperRef.sRGBHex copies the field name straight off the platform's open() result, so the web API's shape leaks into ours. Other core utilities that carry a single primary value expose it as value (cva, queryParams, and fpsMonitor after #248), so eyeDropper is inconsistent with the rest of the API.

Proposed solution

Rename the ref member to match the rest of the API, with a temporary deprecation window instead of a hard break.

New API:

import { eyeDropper } from '@signality/core';

readonly picker = eyeDropper();
// picker.value()      (was picker.sRGBHex())
// picker.isSupported()
// picker.open() / picker.close()

Renames:

Before	After
EyeDropperRef.sRGBHex	EyeDropperRef.value

Alternatives considered