Add curator Movement links config with proof URLs and admin-gated delete votes.

Persist lineage in PostgreSQL, seed documented edges, and keep timeline/tree consumers API-backed with a static fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

db/migrate-movement-links.sql

@@ -0,0 +1,37 @@
+-- Art-movement predecessor → successor edges for timeline / Tree of Art.
+-- Curators manage these with a required proof URL (literature or web essay).
+
+CREATE TABLE IF NOT EXISTS movement_lineage_links (
+  id SERIAL PRIMARY KEY,
+  source_movement_id INTEGER NOT NULL REFERENCES art_movements(id) ON DELETE CASCADE,
+  target_movement_id INTEGER NOT NULL REFERENCES art_movements(id) ON DELETE CASCADE,
+  link_year_approx INTEGER,
+  proof_url TEXT NOT NULL,
+  proof_label TEXT,
+  notes TEXT,
+  created_by INTEGER REFERENCES users(id) ON DELETE SET NULL,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+  CONSTRAINT movement_lineage_links_distinct CHECK (source_movement_id <> target_movement_id),
+  CONSTRAINT movement_lineage_links_unique UNIQUE (source_movement_id, target_movement_id)
+);
+
+CREATE INDEX IF NOT EXISTS movement_lineage_links_source_idx
+  ON movement_lineage_links (source_movement_id);
+CREATE INDEX IF NOT EXISTS movement_lineage_links_target_idx
+  ON movement_lineage_links (target_movement_id);
+CREATE INDEX IF NOT EXISTS movement_lineage_links_year_idx
+  ON movement_lineage_links (link_year_approx);
+
+CREATE OR REPLACE FUNCTION movement_lineage_links_touch_updated_at()
+RETURNS TRIGGER AS $$
+BEGIN
+  NEW.updated_at = now();
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+DROP TRIGGER IF EXISTS movement_lineage_links_updated_at ON movement_lineage_links;
+CREATE TRIGGER movement_lineage_links_updated_at
+  BEFORE UPDATE ON movement_lineage_links
+  FOR EACH ROW EXECUTE PROCEDURE movement_lineage_links_touch_updated_at();