Extract the pure Meta AI SSE/JSON response parsing + content/reasoning/error extraction
(parseMetaSseFrames, readMetaJsonPayloads, collect*/extract*/classify* helpers,
parseMetaAiResponseText, isRecord, the reasoning/renderer key arrays, MetaSseFrame/
ParsedMetaAiResponse types) verbatim into the leaf muse-spark-web/response-parser.ts.
Host imports back the 3 it uses; all module-private (no re-export).
Host 1301 -> 925 LOC. Byte-identical bodies (verbatim), leaf has zero imports (no cycle).
Conversation cache, cookie/auth, fetch, executor class untouched. Adds a split-guard;
consumer tests stay green (muse-spark-cookie-copy-5449 2, muse-spark-web-continuation 6).
