Workspace rows: numbered tab chips with agent status #515

A workspace row shows how many tabs it has, but not which tab needs attention. With several agents in one workspace (one per tab), you only see that something in the workspace is working or blocked once you expand it or open the tab bar. The row itself has room to say more.

Proposal: replace the tab count with one small numbered chip per tab.

• The number is the Herdr tab number and the chip is colored by the most urgent agent state in that tab, in the existing attention order: blocked red, working yellow, done blue, idle or no agent muted.
• The focused tab gets a border. The tooltip shows the number, label and state (1: Implementation · Working).
• Clicking a chip opens that tab. For a workspace on another server in the All servers view, it opens the tab through the existing openServerSession path.
• Up to six chips. When the row is narrower (long workspace name, narrow sidebar), chips fold into a +N marker, down to one chip plus +N. Width is measured with a ResizeObserver, so it follows sidebar resizing.

I have this working on a branch (a workspaceTabChips helper with unit tests, a DOM test, and FEATURES.md), built on #514, which keeps the server badge in the right column. The initial JS grows by about 1.9 KiB and stays under the current budget. Happy to open a PR if this direction fits, or adjust the design first.