* studio: report the true reasoning duration and fix the Stop button for thinking models
For a local GGUF the "Thought for N" label was timed entirely on the client by a
brittle edge-detector, so an always-think model (Qwen3 MTP) that buffers its whole
reasoning and flushes it in one chunk showed "1 second" instead of the real
minute-plus. The client cannot time reasoning it receives atomically, so make the
timing backend-authoritative.
Backend: generate_chat_completion_with_tools measures wall-clock reasoning and
emits a Studio reasoning_summary event (duration_ms) at the moment reasoning ends
-- the first answer token, or end-of-stream for a reasoning-only reply -- for both
the tool-detection pass and the final-answer pass. Timing resets per tool
iteration so the final answer's thinking time wins on the client (which takes the
latest reasoning_summary). routes/inference.py forwards the event in the GGUF tool
stream.
Frontend: parse the reasoning_summary SSE into a _reasoningDurationMs chunk and
use it as the authoritative reasoning duration (last write wins), clamped to >= 0
and guarded to a finite number so a malformed or proxied chunk cannot produce a
NaN label; the persisted value wins for the final "Thought for N" label, with the
previous live timer kept only as a fallback when no metadata arrives.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
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