- rootUnion: decline a schema carrying BOTH oneOf and anyOf rather than
reading one and silently dropping the other's constraints.
- SchemaForm: handle `const` before every type dispatch and for every
constant type, so a numeric/boolean constant, or a schema carrying both
`const` and `enum`, can no longer offer a forbidden value.
- collectSchemaDefaults / TUI initialValue: `const` outranks `default`,
which is an annotation a schema may set to something its const rejects.
- convertToolParameters: resolve from the first branch's merged schema, so a
branch's specialization of a root-declared property is what types the arg.
- TUI: ink-form keys values by field name across the whole form, so two
branches' `kind` were one field and the later section's initial value
decided what the earlier submitted. Branch fields now render under prefixed
names behind a Variant select, and decodeFormValues translates back on
submit, dropping every branch but the chosen one.
Signed-off-by: cliffhall <cliff@futurescale.com>