Team merge — undo a dispatch and restore the original combined team section

[shouze]

Problem

After dispatching repos or extracts to individual teams (#86), the user may want to revert one or more items back to their original combined section (e.g. squad-frontend + squad-mobile), either to correct a mistake or because the dispatch decision is no longer relevant.

Depends on

• Team dispatch — split a multi-team section by assigning each repo/extract to exactly one team #86 (team dispatch infrastructure — dispatchedTeam / extractDispatchedTeam on RepoGroup)

Proposed design

TUI — in dispatch mode

While in dispatch mode (t), pressing 0 (or u) on an already-dispatched item clears its dispatchedTeam / extractDispatchedTeam override, moving it back to the original combined section immediately.

CLI — no new flag needed

Omitting --dispatch for a ref is the default (merged) state. The replay command simply omits --dispatch for un-dispatched items. Merging in non-interactive mode is therefore implicit and lossless: re-running a replay command that lacks a --dispatch entry for a ref is equivalent to having merged it.

This means this issue ships primarily as a TUI interaction; the CLI surface requires no changes beyond what #86 already introduces.

Acceptance criteria

• In TUI dispatch mode, 0 / u on a dispatched item restores it to the original combined section
• The replay command does not emit --dispatch for un-dispatched items (merge = absence of dispatch)
• Re-running the replay command after a merge produces the correct combined-section output
• bun test, bun run lint, bun run knip all pass
• bun run docs:build completes without errors

Documentation

No new pages or sections needed. Two files must be updated:

• docs/usage/team-grouping.md — in the ## Team dispatch section introduced in Team dispatch — split a multi-team section by assigning each repo/extract to exactly one team #86, add a short ### Undoing a dispatch (merge) subsection explaining that 0 / u in dispatch mode restores the item to the combined section, and that the absence of --dispatch in a replay command is equivalent to a merge.

• docs/reference/keyboard-shortcuts.md — in the ### Dispatch mode bindings table introduced in Team dispatch — split a multi-team section by assigning each repo/extract to exactly one team #86, add rows for 0 (restore item to combined section) and u (same action, alternative binding).