Why: implement the reviewed I3 increment - continuous body reading with
per-section status lines, version summary with collapsed line-diff (backend
versions projection from RDM PR #420), right evidence panel with
sources/history/impacts/conflicts tabs, panorama-reader positioning on the
shared selection, per user+project view preferences (panorama/reader,
density, panel tab), strict-seq history merging and honest restricted states.
Evidence: 10 new pure-logic tests (prefs validation, version summary and
diff marks, strict history merge drops, reader assembly three-state); vitest
324/324 green; tsc and vite build green; tokens-only styles.
Impact: cockpit-only; no fourth column, no standalone graph (relations stay
in the right panel); reader entry is explicit (panorama button / view toggle).
Refs: rollout I3
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