feat(embeddings): add embedding model support and related changes

* Introduced EmbeddingModel method in Client and Provider interfaces
* Updated InsertThought and SearchThoughts methods to handle embedding models
* Created embeddings table and updated match_thoughts function for model filtering
* Removed embedding column from thoughts table
* Adjusted permissions for new embeddings table

migrations/007_embeddings_table.sql

@@ -0,0 +1,16 @@
+create table if not exists embeddings (
+  id        bigserial   primary key,
+  guid      uuid        not null default gen_random_uuid(),
+  thought_id uuid       not null references thoughts(id) on delete cascade,
+  model     text        not null,
+  dim       int         not null,
+  embedding vector      not null,
+  created_at timestamptz default now(),
+  updated_at timestamptz default now(),
+  constraint embeddings_guid_unique          unique (guid),
+  constraint embeddings_thought_model_unique unique (thought_id, model)
+);
+
+create index if not exists embeddings_thought_id_idx on embeddings (thought_id);
+
+alter table thoughts drop column if exists embedding;