#3924 feat(host): follow the workspaces list over Neon Realtime

The host follows the workspaces list on liveRows instead of reading it on focus and after writes. Stacked on #3915.

• The follow (workspaces-follow.ts, and followWorkspaces in compose-tasks.ts) runs from the first TASKS_REFRESH after a launch or sign-in until sign-out, and writes each change onto the tasks view. Every window and web tab already hears that view.
• Held polls: with Realtime off it polls through #4272's held read (the after digest), so a change lands in about a second.
• Seals name the account (?userId=). A signed-out answer stops the follow; any other failure is resealed on the board's backoff.
• Removed: the workspaces read on focus, the once-a-minute bound, and the re-read after every workspace write. A rename or a photo still draws the service's answer at once.
• GitHub connection: the account's GitHub-connection check is compared against the clock, so it can't be live. It stays a one-off read on refresh and focus, at most once a minute.

Tests

compose-tasks.test.ts:

• a teammate's change lands
• a failed subscription is polled until it's resubscribed
• a seal that goes unanswered shows reading while the tasks still draw
• one follow stands across refreshes, focus and writes until sign-out

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