Related to FE-4109.
## Summary
- **API codegen workaround**: Platform API's `notebook` content type
hasn't shipped to the OpenAPI spec yet, so `pnpm api:codegen` can't be
run. Locally widened `ContentBase.type` to include `'notebook'` (marked
with TODO for removal once spec publishes).
- **Notebook schema & type system**: Introduced Zod schemas mirroring
RFC-defined notebook shape (`schema_version: 1, cells: Cell[]`).
Maintains wire/domain boundary (cell `sql` → `unchecked_sql` branded for
security). Agent-writable schema for `create_notebook` tool omits cell
IDs (backend-generated); future update operations will require them. All
TypeScript types are `z.infer`'d from schemas (no hand-written parallel
interfaces).
- **IsoDateTimeString moved**: Extracted ISO datetime validator from
`querySource.ts` to `lib/iso-datetime.ts` (data layer shouldn't import
from components layer). Needed by notebook `time_range` fields.
## Test plan
- [x] Unit tests: `notebook-schema.test.ts` (9 tests),
`iso-datetime.test.ts` (3 tests), `querySource.test.ts` updated and
passing (26 tests)
- [x] Typecheck: no new errors
- [x] Prettier: formatting clean
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Added support for validating and processing notebook content,
including markdown, database, log cells, time ranges, and chart
configurations.
- Added compatibility for notebook content types in content handling.
- Added reliable ISO date-time validation for notebook data and related
features.
- **Tests**
- Expanded coverage for valid and invalid notebook structures, cell
requirements, time ranges, chart settings, and date-time values.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Co-authored-by: Joshen Lim <joshenlimek@gmail.com>
