Surface timeline export buttons in the UI

[gauthierpiarrette]

Problem
The backend already implements three export formats for timeline entries - export_jsonrpc(), export_curl(), and export_python() — but the frontend never calls them. These are fully working but invisible to users.

Proposed solution
Add a row of copy buttons to each expanded timeline entry:

• Copy as JSON-RPC — raw JSON-RPC 2.0 payload
• Copy as curl — ready-to-paste curl command
• Copy as Python — session.call_tool(...) snippet

Each button copies to clipboard and shows a brief "Copied!" toast. This turns the timeline from a log viewer into a code generator.

Note: HTTP endpoints will need to be added to the server to expose these methods before the frontend can call them.

Alternatives considered
A single "Export" dropdown instead of three buttons. Three inline buttons are more discoverable and match the "one click" philosophy.