feat(tasks): per-member PR/CI rows + update-all for multi-repo tasks

[kaceper11]

Summary

Multi-repo tasks only polled PR state for the host worktree — member repos' PRs/MRs were invisible on both the Git tab and the board. This adds per-member PR/CI visibility and a one-shot "update all repos" action, stacked on azure-devops (simion#351).

Per-member PR/CI

• New task_member_pr_status command: polls each non-host member's checkout by its live branch (git branch --show-current), so repo_root members track what's actually checked out rather than a frozen recorded branch. Same remote→provider resolution and status vocabulary as the host lookup (github/gitlab/azure).
• pr.refresh() now fires host + member lookups together (Promise.allSettled) — a dead remote on one side can't freeze the other, and a failed member call keeps the last snapshot.
• Git tab: member rows under the PR card — repo · branch, state pill, #42/!42 ref, CI chip, open-in-browser. Rendered for main-checkout tasks too (host card stays hidden there, so this is the only PR surface).
• Board: card footer shows up to 3 member mini-rows + +N more; board mount seeds discovery.
• Poll triggers respect main-checkout semantics: prRelevant = host PR, or member PRs for main-checkout multi-repo tasks; MemberPrRows runs its own tick only when PrCard isn't mounted.
• Staleness guards: member snapshots are dropped if the composition changed mid-flight, and a setLookup landing mid-refresh isn't clobbered by the stale response.

Update all repos

• New task_git_update_all(id, mode): pull / merge-base / rebase-base across host + every on-disk member, each on its own repo_base_branch, via the existing git_update_repo (fetch + autostash + conflict detection). Per-repo results; one failure never aborts the batch.
• Branch-chip dropdown gains an "All repos" section; summary toasts distinguish updated / already-current / needs-attention, localized (en + zh-CN).
• Shared on_disk_members helper is the single contract for "which members are real checkouts" — skips missing paths and any legacy record pointing at the host — used by task_git_status, member PR lookups, and update-all.

Test plan

• tsc -b, cargo check, cargo test — clean
• Vitest: 177 files / 2662 tests — incl. new coverage: single-member gating, main-checkout member polling, member removal mid-flight, setLookup races, host-fail/member-ok allSettled, prFocusEligible, Rust tests for on_disk_members + live-HEAD member lookups
• Manual: member rows verified rendering in Git tab and on board card (injected mock + real repo pills on a multi-repo task)

Out of scope (deliberate)

• Per-member PR creation (task_pr_create stays host-only), per-check CI details, remote picker, member PR background polling on unfocused tasks.

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[kaceper11]

Superseded: opened against simion/termic instead (stacked on simion#351).