feat(workspace): leader dual workspace with auto-copy to team on delegate

- Revert leader workspace override: leader keeps personal workspace as
  default, team workspace accessible via ToolTeamWorkspaceFromCtx
- Auto-copy: when leader creates team_tasks, scan subject+description
  for file paths → copy from personal to team workspace so members can
  access them
- Safety: Lstat (reject symlinks), 10MB size cap, .env excluded from
  allowed extensions, path traversal blocked
- Prompt hint: clarify members can only access team workspace files,
  referenced files are auto-copied

internal/agent/loop_context.go

@@ -167,9 +167,8 @@ func (l *Loop) injectContext(ctx context.Context, req *RunRequest) (contextSetup
 				slog.Warn("failed to create team workspace directory", "workspace", wsDir, "error", err)
 			}
 			ctx = tools.WithToolTeamWorkspace(ctx, wsDir)
-			if team.LeadAgentID == l.agentUUID {
-				ctx = tools.WithToolWorkspace(ctx, wsDir)
-			}
+			// Leader keeps personal workspace (set at line 110-132) as default.
+			// Team workspace accessible via ToolTeamWorkspaceFromCtx for delegation.
 			if req.TeamID == "" {
 				ctx = tools.WithToolTeamID(ctx, team.ID.String())
 			}