feat(schema): derive utoipa::ToSchema on Field/Schema family + alias FieldBase<M>

[shiba4life]

Summary

Phase 3 slice 3 of cross-repo API typegen unification. Closes the upstream half of fold_db_node Phase 4d'.

Adds `utoipa::ToSchema` to the transitive types referenced by the Schema/Field family that fold_db_node wants to register in its `openapi.rs`:

• `FieldType` (`schema/types/field/common.rs`)
• `FieldAccessPolicy` + `AccessTier` (`access/types.rs`)
• `CapabilityKind` + `CapabilityConstraint` (`access/capability.rs`) — transitive deps of `FieldAccessPolicy`
• `DataClassification` (`schema/types/data_classification.rs`)
• `FieldValueType` (`schema/types/field_value_type.rs`) — transitive dep of `DeclarativeSchemaDefinition.field_types`

Adds `#[aliases(...)]` on `FieldBase` for the four molecule variants:

• `FieldBaseSingle = FieldBase`
• `FieldBaseHash = FieldBase`
• `FieldBaseRange = FieldBase`
• `FieldBaseHashRange = FieldBase`

Resolves the `DeclarativeSchemaType as SchemaType` alias quirk in `declarative_schemas.rs` (same class as #679's `super::KeyMetadata` fix). The file-level alias is removed; usages collapse to the canonical `DeclarativeSchemaType` in struct fields, constructor params, match arms, and tests. The unrelated utoipa-internal `SchemaType` at line 92 is preserved.

`FieldMapper` is intentionally not touched — it already has a hand-written `ToSchema` impl that emits `type: string` per its `serde(into = "String")` contract.

Why

After this lands and bump-cascades to fold_db_node, the following $refs go from unresolved to resolved during `npm run generate:api`:

• `DeclarativeSchemaDefinition.{schema_type, source, field_access_policies, field_data_classifications, field_mappers, field_types}`
• `FieldCommon.{access_policy, field_mappers, transform}`
• `{Single,Hash,Range,HashRange}Field/allOf/0`

This closes the loop fold_db_node Phase 1.5 (#790) had to leave dangling and that Phase 4d (#801, atom-module family) couldn't reach because of these transitive ToSchema gaps.

Parent: gbrain `projects/api-typegen-unification`. Recipe: gbrain `projects/register-schema-field-bodies`.

Test plan

• `cargo fmt --all` clean
• `cargo clippy --workspace --all-targets -- -D warnings` clean
• `cargo test --workspace --all-targets` — 662 core tests + observability/etc. green, no regressions
• CI green
• Bump cascade picks this up automatically (schema_service hop ~10 min, fold_db_node hop within 2h cron)

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