feat(studio): add thirteen presets and preview reviewed proposals

docs/releases/2026-10-19-studio-presets-and-proposal-preview.md

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+# Studio 0.1.3: presets and proposal previews
+
+The Studio now offers 13 presets in both its starting and comparison menus.
+The three existing engine presets and public engine API remain unchanged. Ten
+Studio choices add distinct palettes, fonts, corner shapes and panel treatments.
+All 13 validate and compile in light and dark mode; the preview regression test
+renders all 26 combinations using real contracted components.
+
+The first valid generated alternative automatically appears in the main preview.
+Review switches that preview without modifying the draft. Its label identifies
+the reviewed proposal; Show current draft returns to the saved design. Accept
+still creates an ordinary recoverable, undoable revision. New designs start from
+the selected preset instead of an empty token map. Existing empty drafts remain
+untouched and can still be edited or replaced explicitly.
+
+Provider instructions now explicitly describe flat dotted token names, complete
+typed token objects for additions, and mode overrides. A regression test rejects
+nested color groups on an empty draft, then validates three repaired proposals.
+Validation, lock checks, the single repair attempt and deadlines remain enforced.
+
+## Live APIMart verification
+
+On October 19, the deployed 60-second configuration returned three valid proposals
+in one APIMart attempt using gpt-6-luna: Square — 0px, Rounded — 8px, Soft — 16px.
+The brief requested a booking website and these three specific control shapes.
+Their frames rendered in the deployed Studio. The exported generation report was
+independently checked: three distinct canonical designs, zero schema diagnostics,
+and successful compilation of every proposal in both light and dark modes.
+No server key was copied or inspected.
+
+Earlier broader requests in this session produced an invalid nested token group
+and a provider failure. They preserved the draft and prior alternatives. The
+successful constrained request establishes real provider connectivity and valid
+output, not universal success for arbitrary briefs. The improved provider prompt
+and main-preview behavior require deploying 0.1.3 before live verification.
+
+Browser checks of the new local client cover automatic first-proposal preview,
+switching reviewed proposals, acceptance and undo. HTTP success alone is not
+treated as proof of visible preview rendering.