feat: agent and CLI control plane for sessions, worktrees, and scheduled tasks (#2408)

Add a shared OpenChamber control service with two thin adapters — a native
`openchamber` tool injected into managed OpenCode, and new CLI commands — so
users can manage parallel sessions, worktrees, and scheduled tasks
conversationally through agents or from the terminal.

Control plane:
- New openchamber-control service owning a fixed action contract:
  projects.list, models.list, session list/create/send/fork/status/messages,
  and schedule list/create/run/delete/toggle. Session and worktree deletion
  and project registration are deliberately not exposed.
- New openchamber-sessions module owning create/worktree/prompt orchestration,
  Goal Mode dispatch, wait semantics (initial idle never counts as completion;
  timeout and cancellation are failures), and explicit partial-failure results.
- Scheduled-task logic extracted into a service shared by routes, CLI, and the
  agent tool.

Agent tool:
- Managed OpenCode gets a materialized plugin registering one typed tool with
  a loopback-only callback, per-child ephemeral bearer (timing-safe, never
  persisted or logged), and abort propagation into the service.
- The ~1.5k-token schema applies progressive disclosure: short descriptions,
  server-side validation returning actionable usage errors, and intent
  guardrails — created sessions/tasks are user-facing work (not age
  self-delegation); worktree/goal/agent/variant/wait are omit-by-default;
  dispatches produce no completion notification, and later result r
  to session.messages, which now returns the authoritative sessionStatus.
- session.create without a user-named model picks from favorites/re
  send/fork omit the selection and the service reuses the target session's
  last user-message model, agent, and variant before falling back t
- An "Agent control tool" setting (default on, Save + Reload to apply)
  disables plugin injection entirely.

CLI:
- New `openchamber session`, `schedule`, `projects`, and `models` commands
  with automatic instance targeting, --wait/--timeout/--last-assist
  worktree flags, and Goal Mode, preserving interactive, non-TTY, --quiet,
  and --json contracts. The control HTTP timeout derives from the w
  instead of the 4-second default.

UI:
- New built-in "Schedule a Task" starter (/schedule-task) running a
  dialogue that defines a task and offers to create it via the tool after
  explicit confirmation; Craft a Goal and Feature Planning gain the
  handoff offer, and guided starters reserve the question tool for concrete
  option choices. Localized in all 10 locales, migrated into custom
  starter lists, hidden on VS Code.
- Sidebar shows CLI/agent-created sessions live via the control eve
- openchamber tool calls render with per-action titles and metadata.

packages/ui/src/lib/i18n/messages/ko.ts

@@ -1761,6 +1761,7 @@ export const dict: Record<I18nKey, string> = {
   'chat.draftPresets.weigh.label': 'Weigh my options',
   'chat.draftPresets.plan.label': 'Start feature planning',
   'chat.draftPresets.craftGoal.label': 'Goal 만들기',
+  'chat.draftPresets.scheduleTask.label': '작업 예약하기',
   'chat.draftPresets.debug.label': 'Debug an issue',
   'chat.draftPresets.review.label': 'Review my changes',
   'chat.draftStarters.add': 'Add a starter',
@@ -1837,7 +1838,9 @@ export const dict: Record<I18nKey, string> = {
   'chat.commandAutocomplete.command.handoffReviewDescription': '생성된 인수인계로 별도의 리뷰 세션을 만들거나 재사용합니다.',
   'chat.commandAutocomplete.command.featurePlanDescription': '새 기능을 위한 대화형 가이드 계획 세션을 시작합니다.',
   'chat.commandAutocomplete.command.craftGoalDescription': '아이디어나 작업을 명확하고 검증 가능한 Goal로 만듭니다.',
+  'chat.commandAutocomplete.command.scheduleTaskDescription': '안내형 대화를 통해 예약 작업을 정의합니다.',
   'chat.chatInput.toast.craftGoalFailed': 'Goal 만들기를 시작하지 못했습니다',
+  'chat.chatInput.toast.scheduleTaskFailed': '예약 작업 설정을 시작하지 못했습니다',
   'chat.commandAutocomplete.command.catchUpDescription': '맥락을 다시 파악합니다: 무엇을 하고 있었고 어디서 이어서 할지.',
   'chat.commandAutocomplete.command.debugDescription': '수정안을 제시하기 전에 버그의 근본 원인을 단계적으로 조사합니다.',
   'chat.commandAutocomplete.command.weighDescription': '결정하기 전에 2~3가지 접근 방식을 장단점과 함께 비교하고 추천을 제시합니다.',