fix(activity): retry intermittent app icon loads

[EzraEllette]

Summary

• retry native Activity app icons after transient image load failures
• use bounded exponential backoff at 0.5s, 1s, 2s, and 4s
• cache-bust each retry and retain the generic app glyph while waiting or after exhaustion

Before / after

Before: app icon request fails -> generic icon for the rest of the render
After:  app icon request fails -> 0.5s -> 1s -> 2s -> 4s -> generic icon
                                  retry   retry  retry  retry

Test plan

• bun run test:vitest components/activity-ledger.test.tsx (39 passed)
• git diff --check