Replace the five variable nodes with one Variables node

A single node now lists any number of variables. Every entry is an output
that reads the current value whenever it is pulled; an entry switched to
Set is also an input and is written when the flow arrives. Exec pins only
exist while at least one entry writes, and all inputs are read before any
write, so one node can swap two variables.

Get/Set variable, Get/Set variables and Variable are gone. Old project
files are converted on load: each old node becomes a Variables node with
the same variables, edges and typed values.

A written port without a typed value now shows the zero of its kind on
the node body, matching what the inspector shows and what the run writes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/core/node-catalog.test.ts

@@ -106,29 +106,18 @@ const CASES: Record<string, Case[]> = {
 
   // variables
 
-  GetVariable: [
-    { name: 'reads a variable', params: { variable: 'speed' }, outputs: { value: 100 } },
-    { name: 'an unknown variable reads as null', params: { variable: 'nope' }, outputs: { value: null } },
-    { name: 'no variable chosen reads as null', outputs: { value: null } },
-  ],
-  GetVariables: [
+  // Reading needs the interpreter, which asks `read` at the moment: see variable-node.test.ts.
+  Variables: [
     {
-      name: 'reads one output per variable it names',
+      name: 'writes the variables switched to Set, each keeping its declared type',
       ports: [
-        { key: 'speed', kind: 'number' },
-        { key: 'nope', kind: 'number' },
+        { key: 'speed', kind: 'number', write: true },
+        { key: 'lives', kind: 'number' },
       ],
-      outputs: { speed: 100, nope: null },
-    },
-    { name: 'without a variable it reads nothing', outputs: {} },
-  ],
-  SetVariables: [
-    {
-      name: 'writes every variable it names, each keeping its declared type',
-      ports: [{ key: 'speed', kind: 'number' }],
-      inputs: { speed: '250' },
+      inputs: { speed: '250', lives: 9 },
+      context: { variables: { speed: 100, lives: 3 } },
       next: 'exec',
-      after: (ctx) => expect(ctx.variables.speed).toBe(250),
+      after: (ctx) => expect(ctx.variables).toEqual({ speed: 250, lives: 3 }),
     },
     {
       name: 'without a variable it writes nothing',
@@ -136,37 +125,6 @@ const CASES: Record<string, Case[]> = {
       after: (ctx) => expect(ctx.variables).toEqual({ speed: 100 }),
     },
   ],
-  SetVariable: [
-    {
-      name: 'writes a variable, keeping the declared type',
-      inputs: { value: '250' },
-      params: { variable: 'speed' },
-      next: 'exec',
-      after: (ctx) => expect(ctx.variables.speed).toBe(250),
-    },
-    {
-      name: 'no variable chosen writes nothing',
-      inputs: { value: 5 },
-      next: 'exec',
-      after: (ctx) => expect(ctx.variables).toEqual({ speed: 100 }),
-    },
-  ],
-  // Reading without a flow needs the interpreter: see variable-node.test.ts.
-  Variable: [
-    {
-      name: 'writes its variable when the flow arrives, keeping the declared type',
-      inputs: { value: '250' },
-      params: { variable: 'speed' },
-      next: 'exec',
-      after: (ctx) => expect(ctx.variables.speed).toBe(250),
-    },
-    {
-      name: 'no variable chosen writes nothing',
-      inputs: { value: 5 },
-      next: 'exec',
-      after: (ctx) => expect(ctx.variables).toEqual({ speed: 100 }),
-    },
-  ],
 
   // references and properties