fix(wpf): harden Timeline interaction and accessibility

[nicolasestrem]

Summary

• activate Timeline restore points by double-click as well as Enter
• read Timeline catalogs away from the UI thread with explicit loading and failure states
• stack Compare cards at narrow widths and honor the Windows animation preference
• add stable theme automation IDs and mark inactive alternative states offscreen
• provide a readable fallback for missing snapshot diagnostics

This is fix set 2 of 4 and is intentionally stacked on #8.

Verification

Build succeeded.
    0 Warning(s)
    0 Error(s)

Passed!  - Failed:     0, Passed:   997, Skipped:     0, Total:   997, Duration: 6 s - WinRestoreKit.Tests.dll (net8.0)

Changed-file solution formatting and git diff --check passed. Added em dash lines: 0.

Computer Use rendered the isolated CodexVerify build and confirmed the populated Timeline and navigation. Input injection into that elevated test process is blocked by Windows integrity isolation, so full interactive verification remains scheduled on the disposable VM after all four stacked fix sets are combined.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Suppress the empty state after a refresh failure

When the initial catalog read throws, RefreshAsync leaves Events empty, records SelectionError, and then sets IsLoading to false. These two conditions therefore make the “No restore points yet” card visible at the same time as the refresh error, incorrectly telling users that no snapshots exist when storage was merely unreadable. Include the absence of HasSelectionError in this trigger so the failure state is shown instead of the empty state.

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[chatgpt-codex-connector]

Preserve computed offscreen state for visible elements

Returning IsOffscreenBehavior.Onscreen for every active element forces UI Automation to report it as onscreen even when it is clipped or below a ScrollViewer viewport. This occurs for active Confirm sections and for the detail card in the new narrow comparison layout, so assistive technology receives incorrect spatial state until the user scrolls to those controls. Return the default/clipping-aware behavior for active elements and reserve Offscreen for inactive alternatives.

Useful? React with 👍 / 👎.