Resolve review #003 nits N1, N3, N4

- N1: number_from_f64 now returns AlkTypeError::Access for non-finite
  floats instead of silently materializing Value::Null. A NaN/Inf in the
  buffer surfaces as a clear access error rather than a misleading
  'expected a number' validation error.
- N3: drop the dead Value::String arm from check_bytes; the materializer
  only ever emits bytes as an array of u8. Update the validation-model
  docs to match.
- N4: fix stale ADR references in doc comments (ADR-096 -> ADR-002,
  ADR-097 -> ADR-003, ADR-098 -> ADR-004, ADR-101 -> ADR-007).

N2 (BastType::alk_kind returning Struct for ) left as documented;
every current caller resolves the ref first, so forcing Option through
the call sites is churn without benefit.

Verification: cargo test --release (411 pass), cargo clippy --all-targets
-- -D warnings (clean), cargo doc --no-deps (clean).

docs/architecture/validation.md

@@ -47,7 +47,7 @@ tree ([`crate::bast::BastDoc`]/[`BastType`]) that checks exactly these:
 | Int64/Uint64 (full range) | `validate_int64`/`validate_uint64` (JSON precision caveat per ADR-005) |
 | Float finiteness (Float32/64) | `validate_float` with `as_f64().is_finite()` |
 | String `maxLength` (byte length) | `check_string` reads the field-level `maxLength` |
-| Bytes `maxLength` (array length) | `check_bytes` accepts `Value::String` and `Value::Array` forms |
+| Bytes `maxLength` (array length) | `check_bytes` accepts the `Value::Array` form (the materializer emits bytes as an array of u8) |
 | RFC 3339 timestamp shape | `validate_timestamp` — non-strict check (matching v0.1.0) |
 | Enum index bounds | `validate_enum` checks `idx < values.len()` — **fixes the v0.1.0 dead constraint** |
 | Union variant dispatch | `validate_union` reads `__discriminator`, looks up the variant, recurses via `validate_typeref` |