fix(dialogs): keep choice actions inside the window

[obazna]

Summary

• size choice dialogs to their content between a 380px minimum and 760px maximum
• keep normal updater actions on one row and wrap them when the platform constrains the window
• leave updater and version-comparison behavior unchanged
• retry transient macOS DiskImages create/verify failures with bounded backoff and visible diagnostics

Reported regression

The four-action update prompt used the generic fixed 380px frame, causing the Later button to paint past the client edge and be clipped.

CI follow-up

The first PR run exposed an existing hosted-macOS DiskImages flake after the app had already published, signed, and verified. An earlier run had failed at the same boundary on the opposite architecture with Resource temporarily unavailable. DMG creation and immediate verification now get three attempts with 2s/4s backoff; partial output is removed before recreation, and persistent failures still fail the job.

Verification

• DialogLayoutTests: 1/1 passed using the exact updater labels
• verifies automatic one-row layout and actual forced 380px containment in both axes
• Release build: 0 warnings, 0 errors
• local full Avalonia suite: 1565/1566 passed; only the existing host-sensitive /dev/video0 normalization case failed
• final-head CI run 33412244627: Linux build/test/package, Windows package/install validation, macOS x64, and macOS arm64 passed
• final-head CodeQL run 33412244592 passed
• behavior, integration, and test reviewers approve exact HEAD 229e587c5

Manual acceptance

Open a four-action choice such as the prompt for a genuinely newer signed release and confirm every action, including Later, is fully visible and clickable.