feat: resizable nodes with width/height persistence

Add NodeResizer to BaseNode so users can drag corners to resize any node.
Persist width/height through the full stack: DB model, schemas, canvas
save/load route, and migration for existing databases.

Add tests covering save, update, clear, and load of node dimensions.

backend/app/db/database.py

@@ -52,6 +52,10 @@ async def init_db() -> None:
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN disk_gb REAL")
         with suppress(Exception):
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN show_hardware BOOLEAN NOT NULL DEFAULT 0")
+        with suppress(Exception):
+            await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN width REAL")
+        with suppress(Exception):
+            await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN height REAL")
 
 
 async def get_db() -> AsyncGenerator[AsyncSession, None]:

backend/app/db/models.py

@@ -42,6 +42,8 @@ class Node(Base):
     ram_gb: Mapped[float | None] = mapped_column(Float, nullable=True)
     disk_gb: Mapped[float | None] = mapped_column(Float, nullable=True)
     show_hardware: Mapped[bool] = mapped_column(Boolean, default=False)
+    width: Mapped[float | None] = mapped_column(Float, nullable=True)
+    height: Mapped[float | None] = mapped_column(Float, nullable=True)
     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)

backend/app/schemas/canvas.py

@@ -28,6 +28,8 @@ class NodeSave(BaseModel):
     ram_gb: float | None = None
     disk_gb: float | None = None
     show_hardware: bool = False
+    width: float | None = None
+    height: float | None = None
     pos_x: float = 0
     pos_y: float = 0
 

backend/app/schemas/nodes.py

@@ -27,6 +27,8 @@ class NodeBase(BaseModel):
     ram_gb: float | None = None
     disk_gb: float | None = None
     show_hardware: bool = False
+    width: float | None = None
+    height: float | None = None
 
 
 class NodeCreate(NodeBase):
@@ -56,6 +58,8 @@ class NodeUpdate(BaseModel):
     ram_gb: float | None = None
     disk_gb: float | None = None
     show_hardware: bool | None = None
+    width: float | None = None
+    height: float | None = None
 
 
 class NodeResponse(NodeBase):