Add right-click View Plan on Dashboard Blocked Process Reports and Deadlocks grids (#880)

[erikdarlingdata]

Summary

• Mirrors the Lite treatment from PR Fix blocked process report plan lookup (#867) #868 (BPR) and PR Add right-click View Plan on Lite Deadlocks grid (#880) #882 (Deadlocks) on the Dashboard.
• Blocking grid gets two context-menu items: View Blocked Plan and View Blocking Plan (BPR XML contains both sides).
• Deadlocks grid gets a single View Plan item. Dashboard's `DeadlockItem` is one row per process, so we find the matching `` in the graph by SPID and try the process-level `sqlhandle` + statement offsets, falling back to each `` in the `executionStack`.
• Plan lookup hits `sys.dm_exec_query_stats` + `sys.dm_exec_text_query_plan` on the monitored server (same instance that hosts the PerformanceMonitor repo DB). The tab label is `Est Plan - SPID N` and the original query text is attached to the plan viewer.
• Completes Port right-click View Plan to Dashboard blocked process reports + Deadlocks grids (Lite & Dashboard) #880 (final two of three grids).

Test plan

• Build clean (0 errors)
• Dashboard → Blocking sub-tab → right-click a row → View Blocked Plan / View Blocking Plan → plan tab opens
• Dashboard → Deadlocks sub-tab → right-click a row → View Plan → plan tab opens
• Evicted plan shows a clear "no longer in the plan cache" message
• Zero-handle / system-context row shows "no resolvable sql_handle"
• Existing Copy / Export / Download XML items still work on both grids

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