v0.1.21 — think-tag stream filter (no more <think> leakage)

Fixed

• <think> tags no longer leak across SSE fragment boundaries. The think-tag stripper ran per stream fragment, so an SSE boundary splitting the tag itself ("<th" + "ink>") leaked the literal tag into the visible output, and a block whose body arrived in later fragments leaked the private reasoning as answer text. A stateful stream filter (createThinkTagStreamFilter) now carries a possible partial tag across fragment boundaries, suppresses everything inside an open block until its close tag, strips orphan close tags, and surfaces a false-partial tail (e.g. a literal "<tho…") as text instead of swallowing it. Wired into both streaming paths — the reasoning-promotion transform (OpenAI clients) and the Anthropic stream transform (Claude Code) — with separate filter instances per source field, so an unterminated block in reasoning can never suppress real content; a reasoning-phase false partial is merged before the first content fragment, preserving order. The synthetic tail chunk before [DONE] is framed as its own blank-line-closed SSE event and carries the stream's id/model metadata (pre-tag adversarial review findings).