typelayer: table CHECK constraints are not evaluated at ingest #727

Found while moving the type layer to chtypes 1.0 in draft PR #712 (branch chtypes-v2).

Problem. Table CHECK constraints are not evaluated at ingest.

• WaveHouse builds the CREATE TABLE it gives chtypes from discovery's columns (system.columns), so no CONSTRAINT … CHECK reaches chtypes.
• A record that violates a table CHECK is accepted, and may be delivered on the stream.
• The server then refuses it at INSERT (code 469), and the worker parks it.

This was already the case before #712 (main does not evaluate table CHECKs at ingest either), so it is not a regression.

Evidence.

• Measured by a probe of the chtypes 1.0 artifact during feat(typelayer)!: validate, coerce and filter through chtypes #712: chtypes compiles CONSTRAINT … CHECK clauses, and its CHECK verdicts now match the server's. That covers non-UInt8 results refused with code 1, and x > 0 refused with 469, on exactly the rows the server refuses.
• Inferred from internal/typelayer/ddl.go, which emits columns only, and internal/discovery (which reads system.columns; system.tables.create_table_query is fetched but not used for this).

Effect. Clients get 202/200 for records that will never be stored. Stream subscribers can see rows that the table refuses.