fix(sdk): resolve respond() namespace from interrupt id (#2676)

`respond(response, { interruptId })` was sending resumes with the root
namespace whenever `namespace` was omitted. For subgraph interrupts that
mis-targets the resume even though the id already uniquely identifies
the pending interrupt on the thread.
Look the namespace up from `thread.interrupts` by id (same as
`respondAll` / the no-arg path). An explicit `namespace` still
overrides; unknown ids still fall back to root.