fix(web-todo): dock-owned selection, keyboard-openable row, documented tail todos field

Three ds-review-bot round-8 findings on the todo display surfaces.

TodoPanel took the whole `useSession` hook and cast the snapshot to reach
`todos`, which put slot plumbing and an unchecked cast inside the presentation
component. The panel now takes `todos: readonly TodoItem[]`; TodoDock does the
selecting, matching the QueueDock posture the dock slot already establishes.

The todo row carried `onClick` with no keyboard route, so its details panel was
mouse-only. It now takes ToolRow's route verbatim: `role="button"`,
`tabIndex={0}`, and an Enter/Space handler that claims the event. The row stays
a `<div>` because a `<button>` flattens its inline spans.

`session.history`'s tail-only `todos` field was documented at the TS signature
but not in the apiproxy README pair, and the Agent Note claimed the feature
added no new wire vocabulary. Both README sides now state the tail/omission
semantics (an omitted field on a tail response is the empty plan, not unchanged
state), and the note records the one added field instead of denying it.

Tests: TodoPanel specs render the plain list; new TodoDock specs cover selection,
live follow, rollback-to-empty, and the registration shape; a new row spec pins
Enter/Space activation and non-activating keys.

packages/host/apiproxy/README.md

@@ -14,6 +14,8 @@ The mux stream projects the latest log-backed title as a validated `session/titl
 
 Workspace and Session lists are separate reconnect baselines. `workspace.create` creates a unique name or adopts an existing directory, `session.create` accepts an optional preallocated Session id, and `host/workspace-changed` plus `host/session-added` carry committed increments in either arrival order. `SessionSummary.blank` and the `host/session-added` frame carry the derived zero-events bit: clients hide blank sessions and reuse them per workspace, flip blank on the first `host/session-status(running:true)`, and treat `session.list` as the reconnect authority; cold summaries are never blank because lazy persistence keeps never-appended sessions out of `list()`.
 
+`session.history` pages on message boundaries, and its tail page (no `beforeSeq`) carries two session-level extras the page window cannot supply: the in-flight partial's chunk events, and `todos` — the latest `todo/write` whole-list projection over the full log. Older pages omit `todos` because the projection is session-level, not per-page; a tail response that omits it means the whole log holds no `todo/write`, so clients read the absent field as the empty plan rather than as unchanged state.
+
 The `command.*` and `skill.*` domains expose the host command registry and skill catalog to clients. Every method addresses one session's agent by `sessionId` (a served session always has an Agent; `command.*` resumes cold sessions through the same path as `session.*`, while `skill.list` resolves the project root from the session header without touching the Agent registry). `command.execute` runs a slash-command line host-side and returns a detached result; the carrier's request signal cancels the running handler. `host/commands-changed` is the catalog invalidation frame: clients refetch `command.list` instead of diffing.
 
 ## Carrier layer (`/client` + root)