feat: edge edit mode + proxmox container mode toggle

- Double-click any link to open Edit Link modal (type, label, VLAN ID, delete)
- Add updateEdge / deleteEdge actions to canvasStore
- Add container_mode field to proxmox nodes (backend model, schemas, migration)
- NodeModal shows container toggle for proxmox type (defaults ON)
- ProxmoxGroupNode renders as regular BaseNode when container_mode is OFF
- setProxmoxContainerMode store action handles structural changes atomically
  (children parentId/extent, node dimensions)
- CanvasContainer filters edges between container proxmox and its children
- Canvas load respects container_mode when assigning parentId/extent

backend/app/db/models.py

@@ -1,7 +1,7 @@
 import uuid
 from datetime import UTC, datetime
 
-from sqlalchemy import JSON, DateTime, Float, ForeignKey, Integer, String, Text
+from sqlalchemy import JSON, Boolean, DateTime, Float, ForeignKey, Integer, String, Text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.db.database import Base
@@ -33,6 +33,7 @@ class Node(Base):
     pos_x: Mapped[float] = mapped_column(Float, default=0)
     pos_y: Mapped[float] = mapped_column(Float, default=0)
     parent_id: Mapped[str | None] = mapped_column(String, ForeignKey("nodes.id"))
+    container_mode: Mapped[bool] = mapped_column(Boolean, default=False)
     last_seen: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     response_time_ms: Mapped[int | None] = mapped_column(Integer)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)