feat(studio): structured object editors + robust popover viewport clamping

[LeadcodeDev]

User iteration round 5 (screenshots):

1. Popover still clips — now at the window top: the leftward+flip-up fix (feat(studio): optimistic in-memory edits (near-instant canvas) + inspector round 4 #77) doesn't clamp fully. Fix: viewport-aware positioning as a pure, testable geometry function (anchor rect + popover size + viewport → position): prefer below/left, flip when clipping, then CLAMP both axes to the viewport with a margin; escape any scroll-container clipping.
2. No raw JSON objects in the config: stat.trend shows {"value":"+340%","direction":"up","color":null} as a textarea. Complex object fields with known schema properties must render as indented structured sub-rows using the same control factory (String→input, enum→select, color→picker), recursion depth-limited (nested complex → JsonArea fallback). Writes mutate the sub-key and write the whole typed object; null prunes. Number arrays (sparkline_data) get per-entry number rows with add/remove (NumberList, ColorRows pattern).