feat(copilot): finish configuration center

backend/migrations/000056_make_article_embedding_dimension_dynamic.down.sql

@@ -0,0 +1,13 @@
+-- Restore the legacy 1536-dimensional column. Embeddings with any other
+-- dimension cannot be represented and are cleared during rollback.
+ALTER TABLE article_embeddings
+  ALTER COLUMN vector_embedding TYPE vector(1536)
+  USING CASE
+    WHEN vector_embedding IS NULL THEN NULL
+    WHEN vector_dims(vector_embedding) = 1536 THEN vector_embedding::vector(1536)
+    ELSE NULL
+  END;
+
+CREATE INDEX IF NOT EXISTS idx_article_embeddings_vector
+  ON article_embeddings USING ivfflat (vector_embedding vector_cosine_ops)
+  WITH (lists = 100);

backend/migrations/000056_make_article_embedding_dimension_dynamic.up.sql

@@ -0,0 +1,7 @@
+-- Copilot embedding dimensions are configured at runtime. Remove the fixed
+-- vector(1536) typmod so rebuilt article embeddings can use the selected model.
+DROP INDEX IF EXISTS idx_article_embeddings_vector;
+
+ALTER TABLE article_embeddings
+  ALTER COLUMN vector_embedding TYPE vector
+  USING vector_embedding::vector;