feat(inbox): render expandable inbox report card under initial prompt

[rafaeelaudibert]

Summary

When a task is associated with a PostHog inbox report (task.signal_report), the conversation now renders an expandable inbox-report card directly under the initial prompt. You can read the report inline — title, status, summary, priority/actionability — instead of jumping out to the inbox view to read more about it.

What changed

New component — InboxReportCard.tsx

• Fetches the report via the existing useInboxReportById hook (same TanStack Query cache the inbox uses, so it stays in sync — no new data plumbing).
• Collapsed: compact card with a tray icon, report title, and status badge.
• Expanded: the researched summary (SignalReportSummaryMarkdown), priority + actionability badges, and an "Open in inbox" link that resets filters, navigates to the inbox, and selects the report (mirrors the deep-link open path, reusing the warm cache for the detail pane).
• Shows a subtle loading row while fetching; renders nothing if the report isn't accessible.

Wiring (mirrors the existing slackThreadUrl pattern)

• UserMessage.tsx — added an optional signalReportId prop; when present it renders <InboxReportCard> below the message body.
• ConversationView.tsx — passes task.signal_report to UserMessage for the first user message only.

Notes

• The existing [inbox item](posthog-code://…) deep link inside the agent's prompt text is kept — it's part of the prompt the agent reads; the card is an additive UI affordance.
• The card appears on the live/suspended conversation view, not the transient pre-connection PendingChatView.

Verification

• pnpm --filter code typecheck passes clean.
• biome check passes.

🤖 Generated with Claude Code

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 6fa71a2.}

[greptile-apps]

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