[Dashboard] Refresh run history after concurrent runs finish

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

DashboardRunStore keeps discovery results in a one-time Lazy snapshot. A same-application run that is active during the first scan is permanently marked unselectable, and a run created after the scan is never added.

Reopening the run selector cannot discover the completed run until the Dashboard process restarts.

Expected Behavior

Opening or refreshing the run selector should discover newly completed runs and recheck runs that were previously locked.

Steps To Reproduce

1. Start two Run-mode Dashboards for the same application.
2. Load the first Dashboard's run list while the second run is active.
3. Stop the second Dashboard normally.
4. Reopen the first Dashboard's run selector.
5. The completed second run remains absent until the first Dashboard restarts.

Exceptions (if any)

N/A

Aspire doctor output

Aspire CLI 13.6.0-pr.18924.g5ee63941
Windows 10.0.26200

Anything else?

Related to #18924. Source: src/Aspire.Dashboard/ServiceClient/DashboardRunStore.cs:87,185,231-236,336-383. A focused test reproduced the stale result. The issue was also mentioned during PR review and remains on current main.

Start in src/Aspire.Dashboard/ServiceClient/DashboardRunStore.cs at lines 87, 185, 231-236, and 336-383, then run or inspect the focused test mentioned in the issue. Verify the run selector refreshes after a concurrent run finishes, discovers runs created after the initial scan, and rechecks runs that were previously locked.