[9/10] --pick-team-auto: auto-resolve combined sections by common prefix

[shouze]

Context

Resolving a combined/ambiguous team section (e.g. "gamme-lead-client + gamme-lead-client-p1", produced when a repo matches 2+ teams at the same hierarchy level) currently always requires a manual --pick-team "combined label"=chosenTeam assignment (or the interactive p pick mode in the TUI) — see applyTeamPickInTree / resolvePickTeamAssignment in src/group.ts and github-code-search.ts.

Many of these combinations are not actually ambiguous: when one of the combined team names is a literal string-prefix of every other team name in the combo (e.g. gamme-lead-client is a prefix of gamme-lead-client-p1), the "parent" team is the obvious, unambiguous owner. Today this case is not auto-resolved because nestOverlappingLabels explicitly skips any label containing " + " (see its docstring: "Combined-label sections … are never auto-nested"), so the user still has to type the pick manually even though the answer is derivable from the names alone.

This replaces --group-by-team-prefix-consolidate (removed in a sibling issue) as the actual answer to the "reduce manual pick-team busywork" need.

Part of EPIC #125.

Solution

Add a new boolean CLI flag, --pick-team-auto, that automatically resolves combined sections at every hierarchy level using a smallest-common-prefix strategy:

• For each combined section (label containing " + ") at any depth, split the label back into its constituent team names.
• If exactly one of those team names is a literal string-prefix of all the others (the "smallest common prefix" that is itself one of the real candidate names — reusing the same prefix-comparison logic as nestOverlappingLabels), automatically resolve the section to that team, equivalent to an implicit applyTeamPickInTree(sections, path, thatTeam).
• If no team name in the combo is a prefix of all the others (e.g. "squad-frontend + squad-mobile"), leave the section combined and unresolved — same as today. --pick-team remains available (and necessary) for these genuinely ambiguous cases.
• Apply auto-pick before processing any explicit --pick-team assignments, and let explicit --pick-team assignments always win when they target the same section (an explicit pick is a deliberate override of the automatic default).
• Extend resolvePickTeamAssignment's stderr messaging so the "N combined sections still unresolved" note only counts sections that auto-pick could not resolve.
• Thread the flag through the replay command (ReplayOptions in src/output.ts) so a session that used --pick-team-auto reproduces identically.
• Update docs/usage/team-grouping.md (new subsection, replacing "Advanced: consolidated rendering") and docs/reference/cli-options.md.

Acceptance Criteria

• --pick-team-auto automatically resolves a combined section whose team names share a common "parent" prefix, without requiring --pick-team.
• A combined section with no prefix relationship among its team names is left combined/unresolved by --pick-team-auto alone.
• An explicit --pick-team assignment for the same section overrides the automatic resolution.
• Auto-pick applies independently at every hierarchy depth, not just the top level.
• The replay command reproduces --pick-team-auto sessions exactly.
• --format json behavior is unaffected by this flag beyond reflecting the resolved sections (no JSON-specific warning needed, unlike the removed consolidate flag — this changes the actual section membership, not just rendering).

Definition of Done

• Unit tests in src/group.test.ts for the auto-pick resolution function, covering: single common-prefix winner, no common prefix (left combined), 3+-way combos, and nested (non-top-level) sections.
• CLI-level test coverage for flag wiring and replay-command emission (src/output.test.ts).
• docs/usage/team-grouping.md and docs/reference/cli-options.md updated.
• bun test, bun run lint, bun run format:check, bun run knip, bun run build.ts all green.
• Depends on the --group-by-team-prefix-consolidate removal issue being merged first (avoids overlapping churn in github-code-search.ts / src/group.ts).