Update horizon-core input and add missing package overrides (9.8.x)

Refresh horizon-core from 74b53775 (2025-04-16) to 0ce02fa7 (2026-04-02) — picks up the horizon-package-set-lts-ghc-9.8.x merge and ~12 months of upstream activity.

The new horizon-core no longer exposes some packages that were previously available via legacyPackages, so they are declared here in horizon.dhall and regenerated via horizon-gen-nix: constraints-extras, dependent-sum, dependent-sum-template, email-validate, formatting, groups, indexed-profunctors, keys, monad-logger, monad-loops, neat-interpolation, optics-core, pointed, quickcheck-text, rebase, rerebase, stm-chans, string-interpolate, text-conversions, vector-instances.

Also fixes the flake.nix description to match the other lts branches' naming convention (was 'horizon-advance', now 'Horizon Haskell Advance (lts/ghc-9.8.x)').