refactor: enforce mandatory brackets for composite values

Implements Phase 1 and 2 of the syntax rework plan:
- Brackets `[]` are now mandatory for all tuple and array values.
- Removed the `[Type][]` array syntax; arrays now only use `Type[]`.
- `[single]` is now strictly a 1-tuple rather than an array.
- Updated documentation and test fixtures to reflect these breaking
  changes.

csv-loader.md

@@ -146,7 +146,7 @@ Uses [typed-csv](https://github.com/your-repo/typed-csv) syntax:
 | String | `string` | `hello` |
 | Number | `number` | `42` |
 | Boolean | `boolean` | `true` |
-| Array | `string[]` or `[string][]` | `[a; b; c]` |
+| Array | `string[]` | `[a; b; c]` |
 | Tuple | `[string; number]` | `[hello; 42]` |
 
 ## License