HTMX worker activity streaming

Live worker activity updates (depends on t-148 worker observability):

Option A: Polling

• hx-get='/partials/task/:id/activity'
• hx-trigger='every 2s'
• Simple, works everywhere

Option B: Server-Sent Events

• hx-ext='sse'
• sse-connect='/events/task/:id'
• More efficient, real-time
• Requires SSE endpoint in Servant (streaming response)

Start with polling, upgrade to SSE if needed.