Extract the pure content/citation formatters (isThinkingModel, isSearchModel,
cleanDeepSeekToken, formatStreamContent, DeepSeekSearchResult, appendSearchCitations)
verbatim into the leaf deepseek-web/stream-format.ts. Host imports the 5 it uses back
into transformSSE/collectSSEContent (cleanDeepSeekToken stays internal to the leaf).
Host 1147 -> 1108 LOC. Byte-identical bodies (verbatim 34/34), leaf has zero imports
(no cycle), all module-private (no re-export). PoW/auth/token-cache/HTTP dispatch
untouched. Adds a split-guard; consumer tests stay green (deepseek-web 35,
deepseek-web-rolling-window-2942 5, deepseek-web-tools-execute 3).
