feat(channels): default-file channel-less tasks into #me

[k11kirky]

Problem

Tasks created outside a channel (the /code composer, /website/new, the command center) stay unfiled, so they never show up anywhere in the Channels space and work can get lost.

Why

Requested so that every task has a channel home by default — anything not explicitly filed to a bluebird channel should land in the private #me channel instead of disappearing into the unfiled pool.

Changes

• After review feedback: when the project-bluebird flag is on and no channelId/channelName was passed to useTaskCreation (the funnel all composers share), the task is created with its channel set to the user's backend personal channel (channel_type: "personal"). That channel is per-user and provisioned lazily + idempotently server-side, so nothing is shared across teammates and there's no create race. If it hasn't loaded yet the task is created unfiled, as before.
• useTaskChannels gains an enabled option so the channel list is only fetched when the flag is on.
• Instrumented with the existing Channel action event (action_type: "file_task", new surface task_input); added task_input to the ChannelsSurface union.

How did you test this?

• @posthog/ui and @posthog/shared typecheck clean
• Biome check on touched files
• Full @posthog/ui test suite passes (1285 tests / 148 files)

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 7b8bb1f.}

[greptile-apps]

Security Review

The new default filing path can put private #me tasks into a project-scoped /me folder, which can expose tasks between teammates unless the backend enforces per-user ownership for that folder.

_{Reviews (1): Last reviewed commit: "feat(channels): default-file channel-les..." | Re-trigger Greptile}

[github-actions]

Could not verify team-posthog-code membership (GitHub API error). Auto-release is limited to Team PostHog Code members, so this will ship with the next scheduled release instead.