Keep type structure in the compiled schema (fixed array length, f32/f64, unions) #95

Freezing turns a field's type into text (KindValue::Namespaced("T[]", _)), and the text drops information:

• Fixed array length. T[8] and T[] both freeze to "T[]". Generators can't emit [T; 8], nothing checks the length, and validator.rs's detect_cycle (ends_with("[]")) treats every array as a cycle escape, so struct Node { next: Node[4] } isn't caught. schema/idl/size.rs works on the AST instead of the IR because of this.
• f32 vs f64. Both freeze to "float", so comline-rust's map_str_type emits f64 for an f32 field.
• Unions. comline-rust's rust_type has no case for KindValue::Union and emits /* unknown_kind */.

Proposal

Freeze types as a structured value instead of a string: element type, array shape (dynamic, or fixed N), exact primitive. Generators render from that instead of parsing strings with strip_suffix("[]").

This shares a prerequisite with running validators (#96, step 4a: the validate condition also needs freezing as a tree). Doing both in one IR revision means one format bump, not two. .comline/ is CBOR with name-tagged fields, so old stores can still be read with #[serde(default)] where a field is added.

It is also the prerequisite for bounds written on types (#98).

Tasks

• Structured type in FrozenUnit::Field, FrozenArgument, TypeAlias::target, constants
• Keep fixed array length; keep f32/f64 distinct
• detect_cycle: only a dynamic array breaks a cycle
• Generators (generation/codegen kernel, comline-rust, comline-typescript) render from the structured type: [T; N] / fixed tuples or arrays as each target decides, f32 → f32, unions
• size.rs can move to the IR if useful
• Pin cascade (core → generation → comline-rust + comline-typescript → cli → language-server → playground)