fix: address Copilot review round 34 — structured constants, non-required const controls

- A `const` may be an object or an array, with or without a `type`, and
  `String({...})` is "[object Object]" — which no CLI argument can equal, so
  the only value such a schema accepts never matched. Supplied text is parsed
  and compared structurally through the resolver's own comparison (exported as
  `sameJsonValue` so the two cannot disagree), for both branch selection and
  the substitution.
- The TUI's one-option const control is never marked required: its option may
  legitimately be the empty string, which ink-form's required gate can never
  accept, so submission would not even reach `decodeFormValues`. The value is
  fixed by the schema, and `missingRequiredFields` still validates the call.

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/tui/src/utils/schemaToForm.ts

@@ -357,6 +357,12 @@ function buildFields(schema: JsonSchemaObject): FormField[] {
       fields.push({
         type: "select",
         ...baseField,
+        // Never required: the one option may legitimately be the empty string,
+        // which ink-form's required gate can never accept — submission would
+        // not even reach `decodeFormValues`, which reapplies the constant. The
+        // value is fixed by the schema, and `missingRequiredFields` still
+        // validates the decoded call.
+        required: false,
         initialValue: String(pinned),
         options: [{ label: String(pinned), value: String(pinned) }],
       } as FormField);