feat(pgsql): support vector and PostGIS indexes with extensions

* Add handling for pgvector and PostGIS extensions in migration scripts
* Implement operator class and storage parameters for vector indexes
* Update tests to validate new index behaviors and extension creation

pkg/readers/pgsql/README.md

@@ -128,6 +128,27 @@ sessions so they are identifiable in `pg_stat_activity`. If you provide
 - Sequence properties
 - Associated tables
 
+## Extension Types (PostGIS, pgvector)
+
+- Extension column types keep their catalog-formatted form: `geometry(Point,4326)`,
+  `geography(Point)`, `vector(1536)`, `halfvec(768)`, `citext`, arrays included.
+- Built-in types are canonicalized and their dimensions moved to
+  `Column.Length` / `Precision` / `Scale`; extension modifiers stay in `Column.Type`.
+- Index access methods are read from the definition as-is: `gist`, `spgist`, `brin`, `hnsw`,
+  `ivfflat`, `vchordrq`, `vchordg`, `bm25`.
+- Operator class and `WITH (...)` parameters have no model field, so they are stored in
+  `Index.Comment` in the form the PostgreSQL writer reads back:
+
+  ```
+  opclass=vector_cosine_ops; with (m=16, ef_construction=64)
+  ```
+
+  Ordering modifiers (`DESC`, `NULLS LAST`, `COLLATE`) are not treated as operator classes.
+  Numeric parameter values are unquoted (`lists='100'` -> `lists=100`); string values keep
+  their quotes (`key_field='id'`), and dollar-quoted values are preserved whole.
+- Installed extensions are read from `pg_extension` into `schema.Metadata["extensions"]`
+  (only extensions RelSpec recognizes), so a read/write round-trip re-creates them.
+
 ## Notes
 
 - Requires PostgreSQL connection permissions