feat(correlation): ship exact entity clustering in the browser

## Parent

#5981

## What to build

When runtime mode is `exact`, recover correlation cards for signals carrying known registry entities while preserving the current theme fallback and one-signal/one-cluster behavior.

## Acceptance criteria

- [ ] Use one pure shared clustering owner for exact alias-tier resolution, theme fallback, exclusions, dropped-signal accounting, and elapsed time.
- [ ] Keep keyword-tier substring matches out of clustering.
- [ ] Preserve generic oil terms on the theme tier, map explicit WTI to its canonical entity, and keep explicit Brent separate.
- [ ] Carry canonical entity identity separately from display text and use it for entity-tier card identity and trend continuity.
- [ ] Keep `legacy` mode behavior unchanged.
- [ ] Cover single assignment, ambiguous aliases, generic display suppression, same-entity/different-event negatives, and current-card survival.

## Blocked by

- #5982
- #5983

Start by reviewing the exact runtime mode and the work in blocked issues #5982 and #5983; the payload does not name specific files or tests. Done means a shared pure clustering owner satisfies the listed entity, fallback, exclusion, accounting, identity, continuity, legacy-mode, and coverage criteria.

Written by the indexing model from the issue text.