[Subtask] Complete V3 type compatibility for the Hologres catalog

### Describe the subtask

Complete and document the five-family compatibility contract for Hologres.

**Compatibility outcomes**

- **Nanosecond timestamps:** Reject because Hologres precision limits are below 9.
- **Variant:** Reject.
- **Unknown/Null:** Reject.
- **Geometry:** Reject because current spatial JDBC reload loses subtype, SRID, and CRS semantics.
- **Geography:** Reject because current spatial JDBC reload loses subtype, SRID, CRS, and edge semantics.

**Acceptance**

- Reproduce all five families through the connector's public create/conversion path and its alter/load paths where supported.
- A supported mapping must round-trip without losing type identity or parameters.
- An unsupported mapping must return `IllegalArgumentException` before external metadata mutation; no fallback to a narrower or opaque type is allowed.
- Cover nested types where the connector supports complex columns.
- Add focused converter/operation tests and an integration or no-side-effect test appropriate to the connector.
- Update the connector documentation with a five-family compatibility matrix and rejection rationale.
- Keep implementation commits atomic by connector and type family.

**Connector-specific verification**

Cover converter, operation, and no-side-effect paths. Run the module tests and keep cloud integration verification credential-gated with its required environment documented.

**Documentation**

`docs/jdbc-hologres-catalog.md`

### Parent issue

#12056