fix: build Path<Struct> parameters from fields(), not scraped properties

[Kilerd]

Problem

Since the schema-collection mode landed, every operation is generated inside a registry::collect scope, where a derived struct's generate_schema() returns a bare $ref (registering the real schema under components/schemas). Path<T>::generate detected the struct case by scraping properties out of the generated schema — a $ref carries no properties, so it fell through to the simple-type branch:

• the first URL parameter got the whole object's $ref as its schema, and
• every other field of a multi-field path struct was dropped from the documented parameters.

Query<T> was unaffected because it already reads T::fields() first, which is registry-independent.

Fix

Align Path<T> with Query<T>: read T::fields() first, emitting one path parameter per field with its own schema, requiredness and description — identical output inside and outside a collection scope. The properties-scraping branch stays as a fallback for hand-written Schematic impls without fields(), and the simple-type branch is unchanged.

Adjacent cases checked: newtype derives don't go through schema_or_ref, so they stay inline; a simple enum as a path segment now documents as a $ref to its string-enum component, which is valid and arguably better.

Tests

Two regression tests in gotcha/tests/test_path_params.rs: a two-field Path<ConnectionPath> must produce two per-field parameters with inline string schemas, both outside and inside a collection scope (the latter failed before this fix with one parameter holding the object $ref).

Verified with cargo test -p gotcha_core --features axum, cargo test -p gotcha --all-features, clippy and cargo fmt --check.