fix(session-ui): align provider error icon with first line

[opencode-agent]

Aligns the provider error icon with the first line of the message instead of the middle of the whole block.

- <div class="flex w-full min-w-0 items-center gap-2">
+ <div class="flex w-full min-w-0 items-start gap-2">
    <Icon name="outline-hexagonal-warning" class="shrink-0 text-v2-state-fg-danger" />

• The icon stays 16px, the same as the 16px line height and the retry card icon. When a retry turns into an error, the icon stays the same size and position.
• error-card.stories.tsx shows one short and one wrapped provider error. The component test checks that the icon center equals the first line's center in both errors, and that the long error wraps.

Real app timeline (setupTimeline e2e harness):

Before	After

Requested by: @iamdavidhill