feat(assistant): implement tool registry and expand assistant capabilities

Introduce a centralized tool registry system for the assistant to manage
executable operations, permissions, and tool catalogs. This refactors
the assistant dispatch logic from a monolithic approach to a modular,
decorator-based registry.

Key changes:
- Implement `AssistantToolRegistry` to handle tool registration,
  permission checks, and safe operation identification.
- Add a suite of new assistant tools: backup, commit, branch creation,
  deployment, health summary, environment listing, LLM operations,
  maintenance, migration, and dashboard searching.
- Refactor `_dispatch.py` and `_llm_planner.py` to utilize the new
  registry for intent resolution and tool catalog building.
- Enhance the LLM planner to support more descriptive clarification
  responses in Russian when intents are ambiguous.
- Update the frontend to support the new tool-based workflow, including
  improved i18n labels for assistant operations and a new step-by-step
  wizard for the migration page.
- Add ADR-0008 to document the architectural decision for the tool
  registry.

backend/src/api/routes/assistant/_tool_task_status.py

@@ -0,0 +1,79 @@
+# #region AssistantToolTaskStatus [C:3] [TYPE Module] [SEMANTICS assistant, tool, status, task]
+# @BRIEF Handler for the "get_task_status" tool — retrieve task status by id or latest user task.
+# @LAYER API
+# @RELATION DEPENDS_ON -> [AssistantToolRegistry]
+# @RELATION DEPENDS_ON -> [TaskManager]
+
+from __future__ import annotations
+
+from typing import Any
+
+from fastapi import HTTPException
+from sqlalchemy.orm import Session
+
+from src.core.config_manager import ConfigManager
+from src.core.logger import belief_scope, logger
+from src.core.task_manager import TaskManager
+from src.schemas.auth import User
+
+from ._resolvers import _build_task_observability_summary, _extract_result_deep_links
+from ._schemas import AssistantAction
+from ._tool_registry import _check_any_permission, assistant_tool
+
+
+# #region handle_get_task_status [C:3] [TYPE Function]
+@assistant_tool(
+    operation="get_task_status",
+    domain="status",
+    description="Get task status by task_id or latest user task",
+    optional_entities=["task_id"],
+    risk_level="safe",
+    requires_confirmation=False,
+    permission_checks=[("tasks", "READ")],
+)
+@belief_scope("get_task_status")
+async def handle_get_task_status(
+    intent: dict[str, Any],
+    current_user: User,
+    task_manager: TaskManager,
+    config_manager: ConfigManager,
+    db: Session,
+) -> tuple[str, str | None, list[AssistantAction]]:
+    """Get task status by task_id or latest user task."""
+    _check_any_permission(current_user, [("tasks", "READ")])
+    entities = intent.get("entities", {})
+    task_id = entities.get("task_id")
+    if not task_id:
+        recent = [
+            t
+            for t in task_manager.get_tasks(limit=20, offset=0)
+            if t.user_id == current_user.id
+        ]
+        if not recent:
+            return ("У вас пока нет задач в истории.", None, [])
+        task = recent[0]
+        actions = [AssistantAction(type="open_task", label="Open Task", target=task.id)]
+        if str(task.status).upper() in {"SUCCESS", "FAILED"}:
+            actions.extend(_extract_result_deep_links(task, config_manager))
+        summary_line = _build_task_observability_summary(task, config_manager)
+        text = (
+            f"Последняя задача: {task.id}, статус: {task.status}."
+            + (f"\n{summary_line}" if summary_line else "")
+        )
+        return (text, task.id, actions)
+    task = task_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail=f"Task {task_id} not found")
+    actions = [AssistantAction(type="open_task", label="Open Task", target=task.id)]
+    if str(task.status).upper() in {"SUCCESS", "FAILED"}:
+        actions.extend(_extract_result_deep_links(task, config_manager))
+    summary_line = _build_task_observability_summary(task, config_manager)
+    text = (
+        f"Статус задачи {task.id}: {task.status}."
+        + (f"\n{summary_line}" if summary_line else "")
+    )
+    return (text, task.id, actions)
+
+
+# #endregion handle_get_task_status
+# #endregion AssistantToolTaskStatus