Remove silent error handling in UI workflows

[JanSmrcka]

Problem

Several UI flows ignore errors (e.g. stage/unstage/refresh), causing hidden state drift and hard-to-debug failures.

Scope

• Replace ignored errors (_ = ...) with explicit handling
• Surface actionable error state in UI status/messages
• Standardize error propagation pattern for UI commands

Acceptance Criteria

• Ignored error count in internal/ui/* is zero
• Stage/unstage/refresh failures are visible to user
• Tests cover at least one failure path per workflow

Why

Silent failures reduce trust and make production debugging expensive.