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/components/session/sidebar/DOCUMENTATION.md

@@ -73,6 +73,7 @@
 - Folder membership may contain both a parent session and its descendants. Rendering treats only the highest assigned ancestors as folder roots because their normal session trees already include assigned descendants; persisted membership remains unchanged for cleanup and move semantics.
 - Sidebar selection holds the clicked row's viewport position across navigation-driven sidebar updates. Wheel or touch input cancels the hold immediately, so programmatic compensation never fights intentional scrolling.
 - Global session subscriptions are structural: create/delete, title, share, archive, directory, parent, and slug changes invalidate the tree. Recency-only `time.updated` changes do not trigger a rebuild. The separate lifecycle rank invalidates ordering only on `settled ↔ active` transitions, with root sessions ranked among roots and child sessions only among siblings of the same parent.
+- CLI/server-created sessions use the low-frequency OpenChamber control event stream to refresh only the created session directory. The same event retriggers bounded worktree discovery so a newly created external worktree gains ownership without a view reload; it does not re-enable broad session or streaming subscriptions.
 - Recent membership includes active root sessions immediately even when their last committed `time.updated` falls outside the 48-hour window. Children and archived sessions remain excluded, and inactive roots remain timestamp-based. The active-ID subscription is disabled while the sidebar is hidden and ignores retry/status detail changes, avoiding streaming-frequency rerenders.
 - Structural updates rebuild grouped nodes only for projects whose local sessions, worktrees, repository state, or branch changed; unchanged project sections preserve references so memoized group/session descendants skip the update wave.
 - Empty successful lists, unresolved loads, and failed loads are separate UI states. Failed groups expose Retry and retain prior data.