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_search_dashboards.py

@@ -0,0 +1,120 @@
+# #region AssistantToolSearchDashboards [C:3] [TYPE Module] [SEMANTICS assistant, tool, dashboards, search]
+# @BRIEF Handler for the "search_dashboards" tool — search and list dashboards from an environment.
+# @LAYER API
+# @RELATION DEPENDS_ON -> [AssistantToolRegistry]
+# @RELATION DEPENDS_ON -> [SupersetClient]
+
+from __future__ import annotations
+
+from typing import Any
+
+from sqlalchemy.orm import Session
+
+from src.core.config_manager import ConfigManager
+from src.core.logger import belief_scope, logger
+from src.core.superset_client import SupersetClient
+from src.core.task_manager import TaskManager
+from src.schemas.auth import User
+
+from ._resolvers import _resolve_env_id
+from ._schemas import AssistantAction
+from ._tool_registry import assistant_tool
+
+
+# #region handle_search_dashboards [C:3] [TYPE Function]
+@assistant_tool(
+    operation="search_dashboards",
+    domain="dashboards",
+    description="Search and list dashboards by name/id from an environment. Shows id, title, and URL for each dashboard.",
+    optional_entities=["environment", "search", "page", "page_size"],
+    risk_level="safe",
+    requires_confirmation=False,
+)
+@belief_scope("search_dashboards")
+async def handle_search_dashboards(
+    intent: dict[str, Any],
+    current_user: User,
+    task_manager: TaskManager,
+    config_manager: ConfigManager,
+    db: Session,
+) -> tuple[str, str | None, list[AssistantAction]]:
+    """Search and list dashboards from an environment."""
+    entities = intent.get("entities", {})
+    env_token = entities.get("environment")
+    search = entities.get("search")
+    page = int(entities.get("page", 1))
+    page_size = min(int(entities.get("page_size", 20)), 100)
+
+    env_id = _resolve_env_id(env_token, config_manager)
+
+    if not env_id:
+        # Show available environments if none specified
+        envs = config_manager.get_environments()
+        if not envs:
+            return ("Нет доступных окружений.", None, [])
+        env_list = "\n".join(f"- {e.id} ({e.name})" for e in envs)
+        return (
+            f"Укажите окружение. Доступные:\n{env_list}\n\n"
+            f"Пример: `покажи дашборды из окружения dev`",
+            None,
+            [],
+        )
+
+    env_map = {e.id: e for e in config_manager.get_environments()}
+    env = env_map.get(env_id)
+    if not env:
+        return (f"Окружение {env_id} не найдено.", None, [])
+
+    client = SupersetClient(env)
+    all_dashboards = client.get_dashboards_summary(require_slug=True)
+
+    # Filter by search term
+    if search:
+        search_lower = search.lower()
+        filtered = [
+            d
+            for d in all_dashboards
+            if search_lower in str(d.get("id", ""))
+            or search_lower in str(d.get("title", "")).lower()
+            or search_lower in str(d.get("slug", "")).lower()
+        ]
+    else:
+        filtered = list(all_dashboards)
+
+    total = len(filtered)
+    start = (page - 1) * page_size
+    page_items = filtered[start : start + page_size]
+
+    if not page_items:
+        if search:
+            return (
+                f"Дашборды по запросу «{search}» в окружении {env.name} не найдены.",
+                None,
+                [],
+            )
+        return (f"В окружении {env.name} нет дашбордов.", None, [])
+
+    lines = [f"📊 Дашборды в окружении **{env.name}** ({total} всего):"]
+    for d in page_items:
+        title = d.get("title", "Без названия")
+        did = d.get("id", "?")
+        slug = d.get("slug", "")
+        slug_str = f" ({slug})" if slug else ""
+        lines.append(f"- #{did} {title}{slug_str}")
+
+    if start + page_size < total:
+        lines.append(f"\n... и ещё {total - start - page_size}")
+
+    actions = [
+        AssistantAction(
+            type="open_route",
+            label=f"Открыть дашборды в {env.name}",
+            target=f"/dashboards?env_id={env_id}",
+        )
+    ]
+
+    return ("\n".join(lines), None, actions)
+
+
+# #endregion handle_search_dashboards
+# #endregion AssistantToolSearchDashboards