Add priority queue to ai-service and STATUS.md workflow

- Introduce async priority queue service in ai-service; all /chat calls now route through it
- Refactor chat router to separate execute_chat (core logic) from the HTTP handler
- Add /queue endpoints (status, pause, resume, cancel) for queue management
- Update ai-service config to use Pydantic v2 model_config style
- Add STATUS.md files for backend, ai-service, doc-service, and frontend
- Document STATUS.md workflow in CLAUDE.md
- Update doc-service documents router and schemas; frontend DocumentsPage and API client

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

features/ai-service/app/schemas/queue.py

@@ -0,0 +1,40 @@
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, field_validator
+
+from app.schemas.chat import ChatMessage, ChatResponse
+
+
+class QueueRequest(BaseModel):
+    messages: list[ChatMessage]
+    max_tokens: int = 2048
+    temperature: float = 0.0
+    response_format: Literal["json", "text"] = "text"
+    priority: Literal["high", "normal", "low"] = "normal"
+
+    @field_validator("messages")
+    @classmethod
+    def messages_not_empty(cls, v: list) -> list:
+        if not v:
+            raise ValueError("messages must not be empty")
+        return v
+
+
+class JobStatus(BaseModel):
+    id: str
+    status: str
+    priority: str
+    position: int | None = None  # number of jobs ahead; None when not pending
+    created_at: datetime
+    started_at: datetime | None = None
+    finished_at: datetime | None = None
+    result: ChatResponse | None = None
+    error: str | None = None
+
+
+class QueueStatus(BaseModel):
+    running: bool
+    paused: bool
+    queue_size: int
+    current_job_id: str | None = None