Restore task action row (diff button) on channel task detail

[k11kirky]

Problem

Opening a task inside a channel (Bluebird Website space) no longer shows the diff button in the top right, so code changes made by the task can't be reviewed from there. Starting the same task from the "New task" tab (the /code space) still shows it.

The unified Bluebird chrome refactor (#3221) moved the task action row — branch selector, review-panel toggle (diff stats badge), handoff, skill buttons, task actions menu — from the code header bar into ContentHeader, which is intentionally mounted only outside /website. WebsiteLayout renders its own title bar with just the breadcrumb, so channel task details lost the whole row.

Changes

• Extracted the task action row from ContentHeader into a reusable TaskHeaderActions component (pure move, no behavior change).
• WebsiteLayout now renders TaskHeaderActions in its title bar when on a channel task detail route, restoring the diff button (and the rest of the row) for channel-filed tasks.

How did you test this?

• Red-green: added WebsiteLayout.test.tsx asserting the action row renders on /website/$channelId/tasks/$taskId and not on other channel routes — failed before the fix, passes after.
• Full @posthog/ui suite: 172 files / 1507 tests pass; pnpm --filter @posthog/ui typecheck and Biome clean.

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 no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 548a51d.}