Fix the MQTT node, suggest message names, and drop Items

- MQTT nodes failed to build: the topic map was renamed to talk in ports, but
  __slots__ still declared the old name, so every MQTT node raised
  AttributeError. Building one of each node type is now a test, since __slots__
  makes this failure invisible until someone places the node.
- Port names offer the messages already in play: everything published is worth
  reading, and an input nobody provides yet is worth publishing. A message only
  connects when both ends spell it the same way, so choosing beats typing.
- Adding a port focuses its name field.
- Dragging onto an input that already reads something offers the extra port as
  well as the replacement — an MQTT or InfluxDB node usually wants both.
- The template's Item model, its routes, screens and table are gone.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WzrvW7rjQbynnhF6pxh6i

frontend/src/client/schemas.gen.ts

@@ -292,131 +292,6 @@ export const HTTPValidationErrorSchema = {
     title: 'HTTPValidationError'
 } as const;
 
-export const ItemCreateSchema = {
-    properties: {
-        title: {
-            type: 'string',
-            maxLength: 255,
-            minLength: 1,
-            title: 'Title'
-        },
-        description: {
-            anyOf: [
-                {
-                    type: 'string',
-                    maxLength: 255
-                },
-                {
-                    type: 'null'
-                }
-            ],
-            title: 'Description'
-        }
-    },
-    type: 'object',
-    required: ['title'],
-    title: 'ItemCreate'
-} as const;
-
-export const ItemPublicSchema = {
-    properties: {
-        title: {
-            type: 'string',
-            maxLength: 255,
-            minLength: 1,
-            title: 'Title'
-        },
-        description: {
-            anyOf: [
-                {
-                    type: 'string',
-                    maxLength: 255
-                },
-                {
-                    type: 'null'
-                }
-            ],
-            title: 'Description'
-        },
-        id: {
-            type: 'string',
-            format: 'uuid',
-            title: 'Id'
-        },
-        owner_id: {
-            type: 'string',
-            format: 'uuid',
-            title: 'Owner Id'
-        },
-        created_at: {
-            anyOf: [
-                {
-                    type: 'string',
-                    format: 'date-time'
-                },
-                {
-                    type: 'null'
-                }
-            ],
-            title: 'Created At'
-        }
-    },
-    type: 'object',
-    required: ['title', 'id', 'owner_id'],
-    title: 'ItemPublic'
-} as const;
-
-export const ItemUpdateSchema = {
-    properties: {
-        title: {
-            anyOf: [
-                {
-                    type: 'string',
-                    maxLength: 255,
-                    minLength: 1
-                },
-                {
-                    type: 'null'
-                }
-            ],
-            title: 'Title'
-        },
-        description: {
-            anyOf: [
-                {
-                    type: 'string',
-                    maxLength: 255
-                },
-                {
-                    type: 'null'
-                }
-            ],
-            title: 'Description'
-        }
-    },
-    type: 'object',
-    title: 'ItemUpdate'
-} as const;
-
-export const ItemsPublicSchema = {
-    properties: {
-        data: {
-            items: {
-                '$ref': '#/components/schemas/ItemPublic'
-            },
-            type: 'array',
-            title: 'Data'
-        },
-        count: {
-            type: 'integer',
-            title: 'Count'
-        }
-    },
-    type: 'object',
-    required: ['data', 'count'],
-    title: 'ItemsPublic'
-} as const;
-
 export const MessageSchema = {
     properties: {
         message: {