Add a Select node that picks one of two values by a condition

Choosing between two values meant a Branch with the whole action
twice behind it, for example two Play animation nodes that differ
only in the animation. Every later change had to be made in both.
Select picks the value, so the action stays single.

- Select is a data node with the inputs condition, false and true
  and the output value. It passes on "true" if the condition holds,
  else "false". An unconnected condition counts as false, and an
  empty picked input gives null.
- The ports are named false and true, not a and b, so nobody has to
  guess which input is which. The order false, true follows Unreal's
  Select and Blender's Switch.
- false, true and value share one type through `sharedType`, like
  First not empty. With two Animation literals plugged in, value
  takes their type and fits Play animation directly.
- Both inputs are always evaluated. Data nodes have no side effects,
  so that does not matter.

Tests:
- ./check.sh: 160 files, 2363 tests, CHECK EXIT 0 (before 2356).
- 5 cases in tests/core/node-catalog.test.ts and 2 in
  tests/core/shared-port-type.test.ts.
- Counter checks: with the inputs swapped all 5 catalog cases fail,
  without sharedType exactly the type test fails.
- No e2e change, the sum stays at 1380.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/node-catalog.test.ts

@@ -843,6 +843,29 @@ const CASES: Record<string, Case[]> = {
       outputs: { value: 5 },
     },
   ],
+  Select: [
+    {
+      name: 'true takes the true input',
+      inputs: { condition: true, false: 'Idle', true: 'Walk' },
+      outputs: { value: 'Walk' },
+    },
+    {
+      name: 'false takes the false input',
+      inputs: { condition: false, false: 'Idle', true: 'Walk' },
+      outputs: { value: 'Idle' },
+    },
+    { name: 'an unconnected condition is false', inputs: { false: 1, true: 2 }, outputs: { value: 1 } },
+    {
+      name: 'an empty picked input gives null',
+      inputs: { condition: true, false: 1 },
+      outputs: { value: null },
+    },
+    {
+      name: 'a value is passed on as it is, even an empty one',
+      inputs: { condition: false, false: 0, true: 5 },
+      outputs: { value: 0 },
+    },
+  ],
   And: [
     { name: 'both true', inputs: { a: true, b: true }, outputs: { result: true } },
     { name: 'one false', inputs: { a: true, b: false }, outputs: { result: false } },