feat(task-board): task activity feed + PR/link cards in task dialog

[rafavalls]

Summary

Extracts the task activity feed and the reworked PR / link cards from the larger kanban-feature-parity branch into a self-contained change (branched fresh off main, so it carries none of that branch's stale-base drift).

Each task now has a change timeline — created, status moves, (re)assignments — rendered as a Linear-style Activity feed in the task dialog, merged chronologically (oldest-first) with any linked agent sessions. The old separate ActivityCard / PullRequestsCard are replaced by:

• Links panel — the task's pull requests (live GitHub state) plus any links found in the description.
• Activity feed — the change timeline + agent-session cards.

What's included

• migration 143 — append-only task_board_activity table (actor + jsonb data payload), FK-cascaded on org + item.
• TASK_BOARD_ACTIVITY_LIST tool + recordActivity / listActivity storage.
• create / update / run-reactions log created / status_changed / assignee_changed events — best-effort: a log write never fails the change it describes.
• Task-dialog redesign: LinksSection + merged ActivitySection (TimelineBlock groups consecutive events onto a connected rail).
• use-task-board-activity hook + query key; en/pt-br i18n.

Scope notes

• Deliberately activity + PR/links only — comments, attachments, sprints, tags, and releases from the parent branch are not included (kept for the parity branch).
• The sprint_changed activity kind is omitted here since sprints aren't in scope.
• Description link extraction targets main's plain-text description field (bare-URL regex), not the parity branch's rich-text editor.

Testing

• bun run check (mesh + e2e), bun run lint, knip, bun run fmt — all clean (the 3 pre-existing tsc failures are missing optional deps satori/resvg/driver.js, unrelated).
• Added packages/e2e/tests/task-board-activity.spec.ts: asserts a fresh task logs exactly created, a status move appends status_changed with {from,to} (oldest-first), and a no-op update logs nothing. Runs in CI (this workspace isn't provisioned for a local full-stack run).

🤖 Generated with Claude Code

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Summary by cubic

Adds a per‑task Activity feed and a Links panel in the task dialog. Shows a clear timeline of task changes and related PRs/URLs to make context easy to scan.

• New Features

  • Append‑only task_board_activity table with recordActivity/listActivity.
  • Logs created, status_changed, assignee_changed from create/update/reactions (best‑effort; never blocks).
  • TASK_BOARD_ACTIVITY_LIST tool and use-task-board-activity hook.
  • Task dialog: Activity feed (timeline + agent sessions) and Links section (GitHub PRs + description URLs).
  • E2E test covers event order and no‑op updates.

• Migration

  • Run migration 143-task-board-activity. No config changes. Existing tasks start showing activity as events are recorded.

^{Written for commit ad8858e. Summary will update on new commits.}