feat(server,web): import and export Trace files in the trace viewer (#73)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/web/src/lib/strings-en.ts

@@ -846,6 +846,11 @@ When done, open index.html in a browser and self-test once.`,
     inProgress: "in progress",
     systemPrompt: "System prompt",
     toolDefs: (n: number) => `Tool definitions (${n})`,
+    exportFile: "Export",
+    importTrace: "Import Trace",
+    importing: "Importing…",
+    /** Client-side pre-check before reading the picked file (same cap as the server's import route). */
+    fileTooLarge: "The file exceeds the 14MB limit.",
   },
 
   benchmark: {
@@ -899,6 +904,9 @@ When done, open index.html in a browser and self-test once.`,
       task_in_progress: "This Session already has a task running.",
       version_conflict: "The snapshot's version is not newer than the current one.",
       invalid_title: "The title is invalid.",
+      invalid_trace: "This file is not a valid Trace file.",
+      trace_session_exists:
+        "This agent already has a Session with that id; a duplicate Trace cannot be imported.",
     },
   },
 };