feat: add activity hover card

[puemos]

Problem

Unread activity currently requires opening the full Activity page, which makes quick review and cleanup slower than it needs to be.

Why: People should be able to scan unread task updates directly from the sidebar and clear them without leaving their current view.

Changes

• Add a delayed, right-aligned hover card containing only unread activity.
• Reuse activity rows for task navigation and individual mark-as-read actions.
• Add mark-all behavior and keep the badge, full feed, and hover cache synchronized.
• Depend on the unread activity API in PostHog/posthog#74214.

How did you test this?

• Biome checks passed for all changed files.
• API client, shared UI, and web-host typechecks passed.
• Focused activity hook, realtime cache, and activity row tests passed (12 tests).

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found 1 issue in 1 file · 1 warning.

1 warning

src/features/canvas/components/ChannelNav.tsx

• ⚠️ src/features/canvas/components/ChannelNav.tsx:25 React 19 API migration can break callers no-react19-deprecated-apis

_{Reviewed by React Doctor for commit f572403.}

[puemos]

Superseded by the backend-independent recent-activity implementation.