Related subjects: migration with CHECK(id1 < id2) for uniqueness, repository with dual-query (no string interpolation), link/unlink use cases with 8 tests.
Edit page: Radix Tabs (Contenu / Classification), themes extracted as immediate-save SubjectThemes component, related subjects with chip+remove UI and Combobox search.
Subject detail: themes and related subjects displayed in header metadata area, 'Voir aussi' links inline.
Also extracts mapRowToEntity from subject repo for reuse, removes themes from SubjectForm (now independent).
