feat(agents): Add Create/Delete Agent functionality

Backend:
- Added POST /city/agents endpoint for creating agents
- Added DELETE /city/agents/{id} endpoint for soft-deleting agents
- Added CreateAgentRequest, CreateAgentResponse, DeleteAgentResponse models

Frontend:
- Added '+ Новий агент' button on /agents page
- Created /agents/new page with full agent creation form
- Added 'Видалити агента' button in agent Identity tab (Danger Zone)

Features:
- Auto-generate slug from display_name
- Support for all agent fields: kind, role, model, node, district, microdao
- Color picker for agent color
- Visibility toggles (is_public, is_orchestrator)
- Soft delete with confirmation dialog

services/city-service/models_city.py

@@ -579,6 +579,48 @@ class MicrodaoOption(BaseModel):
     is_active: bool = True
 
 
+# =============================================================================
+# Agent Management (Create/Delete)
+# =============================================================================
+
+class CreateAgentRequest(BaseModel):
+    """Request to create a new agent"""
+    slug: str
+    display_name: str
+    kind: str = "assistant"  # assistant, orchestrator, specialist, civic
+    role: Optional[str] = None
+    model: Optional[str] = None
+    node_id: Optional[str] = None
+    home_node_id: Optional[str] = None
+    home_microdao_id: Optional[str] = None
+    district: Optional[str] = None
+    primary_room_slug: Optional[str] = None
+    avatar_url: Optional[str] = None
+    color_hint: Optional[str] = None
+    is_public: bool = False
+    is_orchestrator: bool = False
+    priority: str = "medium"
+
+
+class CreateAgentResponse(BaseModel):
+    """Response after creating an agent"""
+    id: str
+    slug: str
+    display_name: str
+    kind: str
+    node_id: Optional[str] = None
+    home_microdao_id: Optional[str] = None
+    district: Optional[str] = None
+    created_at: datetime
+
+
+class DeleteAgentResponse(BaseModel):
+    """Response after deleting an agent"""
+    ok: bool
+    message: str
+    agent_id: str
+
+
 # =============================================================================
 # Visibility Updates (Task 029)
 # =============================================================================