Add effort badge to chain summary

Snapshot the agent's effort onto the chain (like model) so it survives
reload, archive and shared chains, then show it in the chain-end meta line.

- ChainRecord.Effort + chains.effort column (TryAddColumn migration).
- CreateChain INSERT carries the value.
- ChatService snapshots agent.Effort at chain creation, but only for Claude
  models – OpenAI providers store '' so there is no misleading badge.
- Anthropic streaming + CLI done-events include effort for the live path.
- chat.js buildMetaBadges renders "Effort: <level>" after the model badge,
  only when a value is set.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Models/ChainRecord.cs

@@ -20,5 +20,6 @@ public class ChainRecord
     public string ArchiveId { get; set; }
     public string StreamErrorInfo { get; set; }
     public bool PlanMode { get; set; }
+    public string Effort { get; set; }
     public string CreatedAt { get; set; }
 }