[http-specs] Add named-model query parameter scenario to remaining expansion styles for parity

## Background

PR #11125 added a `model` (named model value) scenario for query parameter expansion, but only under `query-expansion/explode`:

- `Routes_QueryParameters_QueryExpansion_Explode_model` — `GET /routes/query/query-expansion/explode/model?field=status&value=active`

This covers the gap behind #11123 / #10973, where a named `model` flows through a different emitter type-handling path than a `Record`.

## Request

For parity with the existing `primitive` / `array` / `record` cases, add the same **named-model** scenario to the other expansion styles that currently lack it:

- `query-expansion/standard` (`{?param}`)
- `query-continuation/standard` (`?fixed=true{¶m}`)
- `query-continuation/explode` (`?fixed=true{¶m*}`)

Each should use a named model value (e.g. `ExpandParameters { field: string; value: string; }`) and add a matching mock API plus regenerated `spec-summary.md`.

_Follow-up requested in [PR #11125 review](https://github.com/microsoft/typespec/pull/11125#discussion_r3505653679)._

Start by comparing the existing query-expansion/explode/model scenario from PR #11125 with the primitive, array, and record cases. Add matching named-model scenarios for query-expansion/standard, query-continuation/standard, and query-continuation/explode, including mock APIs, then regenerate spec-summary.md and verify parity.

Written by the indexing model from the issue text.