feat: agents desktop recordings backend (#23894)

This PR introduces screen recording of the computer use agent using the
virtual desktop.

- Screen recording is triggered by a `wait_agent` tool call. Recording
is stopped by a successful `wait_agent` tool call or when there hasn't
been any desktop activity for 10 minutes.
- Recordings are handled by the `portabledesktop` cli via the `record`
command. The videos are sped up in periods of inactivity.
- Recordings are saved to the database to the `chat_files` table.
There's a hard limit of 100MB per recording. Larger recordings are
dropped.
- A successful `wait_agent` on a computer use subagent tool call returns
a `recording_file_id`, later allowing the frontend to display the
corresponding video.

agent/agent.go

@@ -398,7 +398,7 @@ func (a *agent) init() {
 	gitOpts := append([]agentgit.Option{agentgit.WithClock(a.clock)}, a.gitAPIOptions...)
 	a.gitAPI = agentgit.NewAPI(a.logger.Named("git"), pathStore, gitOpts...)
 	desktop := agentdesktop.NewPortableDesktop(
-		a.logger.Named("desktop"), a.execer, a.scriptRunner.ScriptBinDir(),
+		a.logger.Named("desktop"), a.execer, a.scriptRunner.ScriptBinDir(), nil,
 	)
 	a.desktopAPI = agentdesktop.NewAPI(a.logger.Named("desktop"), desktop, a.clock)
 	a.mcpManager = agentmcp.NewManager(a.logger.Named("mcp"))