feat(chat): task pill and session tabs replace the branch pill

[rafavalls]

Summary

Stack 2 of 3 — targets rafavalls/task-owns-branch (#6424), not main.

The workspace header's context control becomes the task rather than the branch, since a task now owns the branch its sessions share. This is the bulk of the diff.

• TaskPill — switch task, or add the current chat to the board.
• SessionTabs — the task's sessions as tabs, with live per-session status and a "new chat in this task" action.
• TaskCrumb — the linked task, as a crumb back to the board.
• threadStatusStyle / statusPriority move into task-board/config so the board and the session tabs render status identically. A failed run whose failure is settled history (superseded, or died after already delivering — isResolvedRunFailure) no longer paints as an actionable error; painting those red is what made cards the reviewers had approved look broken.
• The task dialog grows a sessions list and comment & re-run, which threads feedback through TASK_BOARD_ITEM_RERUN into the re-run's prompt (the API side is included here rather than split off, since the dialog needs the feedback field to typecheck).

Testing

• tsc --noEmit clean on apps/web and apps/api.
• 28 tests pass across the pills specs and enqueue-super-agent.test.ts.

Notes for the reviewer

task-dialog.tsx is a large diff; the sessions list and the comment & re-run control are the substance, the rest is the surrounding restructure. BranchPill itself is not deleted — branch-picker.tsx still uses it.

🤖 Generated with Claude Code

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Summary by cubic

Switches workspace context from branch to task: the chat header replaces the branch pill with a TaskPill and SessionTabs, plus a TaskCrumb back to the board. Unifies status styling (resolved failures no longer paint as errors) and adds comment & re-run in the task dialog.

• TaskPill: switch task or add the current chat to the board; shows branch in the tooltip; loose chats read “No task.”
• SessionTabs: tabs for a task’s sessions with live per-session status; includes “New chat in this task;” hidden for loose chats.
• TaskCrumb: quick link back to the task on the board.
• Status rendering: move threadStatusStyle and statusPriority to task-board/config; board and tabs render status identically; settled failures (e.g., superseded or after-delivery deaths) no longer render as actionable errors.
• Task dialog: sessions list and “Comment & re-run;” feedback flows through TASK_BOARD_ITEM_RERUN into the rerun prompt; new i18n keys added (en and pt-BR).
• API/tooling: TASK_BOARD_ITEM_RERUN input now accepts optional feedback; rerun prompt copy leads with “Changes were requested;” tests updated. BranchPill remains in use in branch-picker.tsx.

Migration

• If you invoke TASK_BOARD_ITEM_RERUN directly, you may now pass feedback to steer reruns; no breaking change.
• Update any copy assertions expecting “A reviewer requested changes” to “Changes were requested.”

^{Written for commit 946ed06. Summary will update on new commits.}