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.

AGENTS.md

@@ -28,6 +28,7 @@ Build produces separate bundles per entry point (see `tsup.config.ts`). The csv-
 
 - Schema syntax uses **semicolons** (`;`) as separators, not commas
 - Unknown identifiers throw a `ParseError` — only recognized keywords (`string`, `number`, `int`, `float`, `boolean`) and string literals (`"on"`, `'off'`) are valid types
+- Tuple and array **values** must be wrapped in brackets `[]` (e.g. `[a; b]`); `[single]` is a 1-tuple, not an array — use `Type[]` for arrays
 - `@tablename` / `@tablename[]` are reference schemas resolved at CSV load time
 - `csvToModule()` emits accessor functions (`getData()`) for tables with references, and static JSON for tables without; bundler loaders all use `csvToModule`
 - `parseCsv({ resolveReferences: false })` stores reference IDs instead of resolved objects — used by `csvToModule` to emit import-based lazy resolution