fix: align ECR image list columns

[nathanhuh]

Problem

The ECR image list renders tag, digest, pushed time, size, and cleanup status as a single padded string. When tags have different lengths, the digest/SHA column starts at different visual positions, making the list hard to scan.

Scope

Align ECR image list rows into fixed visual columns:

• tag / primary label
• digest
• pushed timestamp
• size
• cleanup status

UX Notes

• Digest/SHA values should start at the same column for every row.
• Preserve selected-row styling, stale/untagged warning styling, and filter highlighting.
• Long tags should truncate or otherwise fit without shifting later columns.
• Keep the list compact and readable in narrow terminals.

Acceptance Criteria

• ECR image rows are visually column-aligned.
• Long tags do not push digest/time/size columns out of alignment.
• Existing stale/untagged indicators still render clearly.
• Tests cover mixed-length tags and verify digest column alignment.