feat: AI Side-Kick ACP UX

[falfaddaghi]

Summary

Adds the Phase B AI side-kick UX on top of the existing OpenCode-shaped ACP bridge, introducing a persistent bottom-right assistant panel for multi-turn workflow help. The implementation includes client-side Nexus action parsing/execution, inline destructive-action approvals, forwarded ACP permission/tool-call rendering, and editor/header/shortcut integration while preserving bridge-based session behavior. It also adds store/runtime tests and an E2E specification for the side-kick review pipeline.

Plan: docs/tasks/ai-sidekick-acp-ux-caa41bd1/plan-ai-sidekick-acp-ux-caa41bd1.md

ADW tracking ID: caa41bd1

Checklist

• Verified and extended bridge/OpenCode API contract for forwarded permission mode and ACP event variants
• Added side-kick domain types, Zustand store state/actions, persistence, and connector invalidation behavior
• Implemented view snapshot and system-prompt helpers for compact context and Nexus action instructions
• Implemented streaming <action> parsing with fenced-code handling and parser coverage
• Added the Nexus client-side action registry with schema validation, collaboration guards, sub-workflow-aware mutations, and destructive action support
• Implemented side-kick runner orchestration for sessions, SSE streaming, action dispatch, follow-up tool results, cancellation, ACP tool cards, and permission responses
• Built the floating side-kick panel, message list, input bar, Nexus action cards, ACP tool cards, and permission cards
• Integrated the side-kick with the workflow editor, header controls, keyboard shortcuts, properties-panel coexistence, and README shortcut documentation
• Added automated side-kick tests for parser, context, tools, and runner behavior
• Added the E2E specification for AI side-kick ACP UX validation

Key Changes

• Introduces src/store/sidekick/ for the side-kick runtime, tool registry, parser, context helpers, system prompt, and tests.
• Adds src/components/workflow/sidekick/ UI components for the floating assistant panel and inline action/permission/tool-call cards.
• Extends OpenCode/bridge-facing types and permission services so side-kick sessions can use forwarded ACP permissions.
• Wires the side-kick into the editor shell, shared header action, Mod+Alt+I shortcut, and properties-panel sizing behavior.
• Documents the new shortcut and adds a task-specific E2E test plan under docs/tasks/ai-sidekick-acp-ux-caa41bd1/.