feat(topology): persist complete diagram semantics

topology_api/migrations/005_layout_presentation.sql

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+-- Persist all presentation semantics required by the database-driven SVG.
+
+ALTER TABLE topology.diagram_nodes
+    ADD COLUMN IF NOT EXISTS display_meta text,
+    ADD COLUMN IF NOT EXISTS display_hint text,
+    ADD COLUMN IF NOT EXISTS decorations jsonb NOT NULL DEFAULT '{}'::jsonb;
+
+CREATE TABLE IF NOT EXISTS topology.diagram_node_members (
+    diagram_node_id uuid NOT NULL
+        REFERENCES topology.diagram_nodes(id) ON DELETE CASCADE,
+    component_id uuid NOT NULL
+        REFERENCES topology.components(id),
+    display_order integer NOT NULL DEFAULT 0,
+    PRIMARY KEY (diagram_node_id, component_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_diagram_node_members_component
+    ON topology.diagram_node_members(component_id);