feat: assistant workspace — persistent AI personality & memory via Markdown files (#165)

Add "Assistant Workspace" feature that lets users designate a directory
(e.g. Obsidian vault) containing 4 Markdown files (soul.md, user.md,
memory.md, claude.md) to define AI personality, user profile, long-term
memory, and execution rules. These files are automatically injected into
the system prompt for assistant project sessions.

Core library (src/lib/assistant-workspace.ts):
- Workspace validation, initialization with template files
- File loading with 8000-char truncation, XML prompt assembly (40k limit)
- State management via .assistant/state.json
- Directory docs generation (README.ai.md + PATH.ai.md)
- Case-insensitive file name fallback (soul.md → SOUL.md)

System prompt injection (src/app/api/chat/route.ts):
- Scoped to sessions where working_directory === workspace path
- Workspace prompt prepended before session-level system prompt
- Onboarding/check-in instructions injected as <assistant-project-task>
- autoTrigger flag skips user message save and title update

Chat-based onboarding (10 questions) & daily check-in (3 questions):
- AI conducts conversation, outputs structured completion code blocks
- Frontend detects onboarding-complete/checkin-complete blocks
- Backend calls Claude API to generate file content from answers
- Fallback to raw answers if API call fails

Auto-trigger pipeline:
- Mount trigger (500ms delay) + focus fallback in MessageInput
- assistantTriggerFiredRef prevents duplicate triggers per mount
- hookTriggeredSessionId in state.json prevents cross-reload duplicates
- Daily check-in only triggers in the most recent workspace session
- hookTriggeredSessionId cleared via __clear__ sentinel after completion

API endpoints:
- GET/PUT /api/settings/workspace — path CRUD + file status
- POST /api/workspace/session — create (onboarding) or reuse (check-in)
- POST /api/workspace/onboarding — AI-generate soul.md + user.md
- POST /api/workspace/checkin — AI-update memory.md + user.md
- POST /api/workspace/hook-triggered — set/clear trigger guard
- GET /api/workspace/latest-session — latest session lookup
- POST /api/workspace/docs — refresh directory documentation

UI:
- Settings "Assistant" tab with workspace path, file status, controls
- Violet badge on workspace project group in ChatListPanel
- useAssistantWorkspace hook for state queries

Also includes:
- 102 passing tests (16 new regression tests for workspace logic)
- i18n keys for en.ts and zh.ts
- Handover documentation and execution plan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/index.ts

@@ -439,8 +439,27 @@ export const SETTING_KEYS = {
   THEME: 'theme',
   PERMISSION_MODE: 'permission_mode',
   MAX_THINKING_TOKENS: 'max_thinking_tokens',
+  ASSISTANT_WORKSPACE_PATH: 'assistant_workspace_path',
 } as const;
 
+// ==========================================
+// Assistant Workspace Types
+// ==========================================
+
+export interface AssistantWorkspaceState {
+  onboardingComplete: boolean;
+  lastCheckInDate: string | null;
+  schemaVersion: number;
+  hookTriggeredSessionId?: string;
+}
+
+export interface AssistantWorkspaceFiles {
+  soul?: string;
+  memory?: string;
+  user?: string;
+  claude?: string;
+}
+
 // ==========================================
 // Reference Image Types (for image generation)
 // ==========================================