fix(ui): align Cancel and Send enabled state

[elagin]

Fixes #5282

This change fixes inconsistent footer action behavior in Channel Config, where Send could appear active without actionable changes and Cancel did not follow the same enabled-state logic.

What changed

• Updated shared PreferenceFooter so both Cancel and Send respect the same enabled state.
• Kept Channel Config as the source of truth for action availability (enabled && isEditing).
• Ensured visual state now matches actual button behavior.

Why

• Prevents misleading UI state.
• Makes unsaved-changes workflow clearer.
• Reduces accidental confusion before leaving the screen.

Validation

• ./gradlew :core:ui:spotlessApply
• Manual check on Channels screen:
  • no edits -> footer actions are disabled
  • after edits -> footer actions are enabled

[CLAassistant]

All committers have signed the CLA.