feat: in-text citations — visual styling, per-unit splitting, ADS search fallback

fix: document _CITE_UNIT.lastIndex reset intent — module-level /g regex footgun

feat: in-text citations — splitCitations, cite spans, slim ref popover, muted styling

feat: references parser + session v2 — corpus matching, citeIndex, new schema models

feat: figure mention popovers with caption annotator

fix: parse CRLF-framed SSE events from sse-starlette

feat: pure note-alignment layout math

feat: frontend session, SSE api client, modes