Refactor cli-v2 session store workflows

[roackb2]

Summary

• split the cli-v2 control-plane session store into a small facade plus focused workflow owners for snapshot state, loading, prompt routing, slash commands, direct shell, approvals, run polling, and live events
• removed private one-line forwarding wrappers from the store facade; callback wiring now points at the owning service/controller directly
• documented the state-layer ownership rules and no-thin-wrapper invariants
• preserved the existing public store API used by Ink components while keeping domain policy in control-plane/client-shared/core owners

Tests

• yarn typecheck
• yarn test src/tests/unit/cli-v2/control-plane-session-store.test.ts src/tests/unit/cli-v2/prompt-activity.test.ts src/tests/unit/cli-v2/runtime-status.test.ts src/tests/unit/cli-v2/file-mention-picker.test.tsx
• yarn build
• rg -n "from '"|from ['"].*(core|server|cli/chat)" src/cli-v2
• rg -n "runShellCommand|shell-process|ConversationDirectShellService|ToolApprovalService" src/cli-v2 src/web-v2

Manual regression surface

• cli-v2 startup, workspace/session loading, and switching sessions
• normal prompt submit, queued prompt submit during active run, and assistant stream rendering
• slash command execution, command result retention, and command-driven session switching/continue
• direct shell preflight, confirmation/cancel/run, and direct shell result activity
• pending approval refresh/resolution, run cancellation, and polling recovery when live events lag
• plan/current activity/latest activity rendering, runtime status bar, and file mention search

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