internal/server,shared: support request metadata (#850)

- add support for http handlers in the request chain to append metadata
to the request
- metrics middleware will include metadata in the activity log 
- update Activity UI to support metadata, drag sort columns
- update Activity UI capture dialog to use more screen space

Updates #834

ui-svelte/src/lib/types.ts

@@ -41,6 +41,7 @@ export interface ActivityLogEntry {
   tokens: TokenMetrics;
   duration_ms: number;
   has_capture: boolean;
+  metadata?: Record<string, string>;
 }
 
 export interface ReqRespCapture {