fix(codegen-kotlin): generated controller filters @filterable field.enum columns (#179)

[dmealing]

Closes #179.

Bug

An Exposed enum column is typed Column<Enum>, but the generated Kotlin Spring controller emitted Table.col eq (p.value as <BareEnum>) for a @filterable field.enum — two compile/runtime defects:

1. the enum type name was un-prefixed (Tier instead of <Owner>Tier) → unresolved reference;
2. even fixed, the filter-value coercer produces a String, so as <Enum> → ClassCastException.

So any entity with a filterable enum column produced a non-compiling controller. Pre-existing; the TPH subtype-fold work (#180) was the first filterable enum to reach a Kotlin controller.

Fix

Filter an enum column by its stored string via CAST(col AS text) (col.castTo<String>(TextColumnType())) — matching every other port's string-band enum-filter semantics (FilterOps grants enum the string ops eq/ne/in/like/isNull; the Exposed column stores the member name as VARCHAR, so the cast compares exactly what the other ports compare).

• columnElementType returns "String" for an enum (the predicate value type the coercer already produces).
• The WHERE arm wraps the column in the cast for eq/ne/in/like; isNull stays on the raw column.
• castTo / TextColumnType imports are added conditionally — on both the vanilla and the TPH controller import blocks — only when a filterable enum column is present, so enum-free controllers stay byte-identical.

Gating

• EnumFilterControllerRunTest — compiles the generated controller and runs eq/ne/in/like filters against H2 (PostgreSQL mode) over MockMvc, asserting the correct rows (not just that it compiles).
• TphFullSuiteCompilesTest — gains a non-discriminator @filterable enum on a subtype (folds into the union), compile-gating the TPH controller's enum-import block (the reviewer's CONFIRMED gap — the TPH path shares emitFilterPipeline but has its own import set).

All green: codegen-kotlin 271/0, api-contract 21/0, TPH 6/0, no snapshot drift (non-enum controllers unchanged).

Two rounds of code review + simplify informed this change.

🤖 Generated with Claude Code