Agent detail page with event stream, interaction, and collapsible thinking

Create the agent detail page showing full output and interaction controls.

Layout

1. Header: Agent name/ID, status badge, task link (if associated), cost, elapsed time 2. Action bar:

• Message input + Send button (for idle agents) — POST to daemon's /agents/:id/send
• Stop button (for running agents) — POST to daemon's /agents/:id/stop
• "Send to review" button (for idle/completed agents with a worktree)

3. Event stream: Full agent output, live-updating via htmx polling

• Thinking blocks: Collapsible, shown with 💭 icon, italic, muted color. Default collapsed.
• Tool calls: 🔧 icon, tool name in accent color, args preview. Expandable to show full args.
• Tool results: 📋 icon, tool name, truncated result. Expandable to show full result.
• Text output: 💬 icon, full text content from assistant messages.
• Errors: ❌ icon, red text.
• Turn boundaries: Horizontal divider with turn number and cumulative cost.
• Steering messages: 🎯 icon, shown when user sent guidance.

4. Sidebar/tabs (on wider screens):

• Diff tab: git diff of worktree
• Files tab: file browser for worktree directory

Event Parsing

The daemon logs pi JSONL events to /var/log/agentd/<run-id>/pi.log. Parse these events similar to Pipeline/Web.hs parseEventLog but with more detail:

• Show thinking content (currently truncated to 200 chars in pipeline — show full, collapsible)
• Show complete tool call arguments (not just summary)
• Show complete tool results (not just truncated)
• Parse message_start, message_update, message_end, turn_start, turn_end, agent_start, agent_end

HTMX

• Event stream div: hx-get="/agents/:id/events" hx-trigger="every 3s" when agent is running/idle
• Stop polling when agent is completed/failed (HTTP 286 pattern from pipeline)
• Message form: hx-post="/agents/:id/send" with hx-swap="none" (no DOM update needed)

Collapsible Thinking

Use <details><summary> for collapsible thinking blocks:

<details class="ev-thinking">
  <summary>💭 thinking...</summary>
  <div class="ev-thinking-content">Full thinking text here...</div>
</details>