httpdomain renderer: block-scalar summary produces unpaired ** and literal asterisks in output

The httpdomain renderer wraps an operation's summary in ** without stripping it first. When the summary comes from a YAML block scalar the value ends in a newline, so the generated markup opens the strong marker on one line and closes it on the next. docutils can't pair it, and the reader sees literal ** on the rendered page.

This is a rendering defect, not just a warning: the asterisks are visible in the HTML output.

Minimal reproducer

spec.yml — note summary: |:

openapi: 3.0.3
info:
  title: Minimal
  version: 1.0.0
paths:
  /thing:
    get:
      summary: |
        Get Thing
      responses:
        200:
          description: A thing.

index.rst:

Page
====

.. openapi:: spec.yml

conf.py:

extensions = ["sphinxcontrib.openapi"]
openapi_default_renderer = "httpdomain"

Actual

$ sphinx-build -W -b html src out
src/index.rst:3: WARNING: Inline strong start-string without end-string. [docutils]

The rendered HTML contains a docutils problematic node with the literal marker:

<dd><p><a href="#id1"><span class="problematic" id="id2">**</span></a>Get Thing

Changing the spec to a plain scalar, summary: Get Thing, makes the warning and the literal ** disappear. That's a viable workaround, but a block scalar is valid YAML for this field and shouldn't break rendering.

Expected

**Get Thing** rendered as strong text, with no warning, regardless of trailing whitespace in the source value.

Cause

sphinxcontrib/openapi/renderers/_httpdomain.py, line 284:

284:            yield f"   **{operation['summary']}**"

With operation['summary'] == 'Get Thing\n' this yields:

   **Get Thing
**

.strip() on the value before interpolation should be enough. Description fields don't have this problem because they go through the markup converter, which normalizes them; summary is interpolated directly.

Worth noting the old renderer handles the same spec without this warning, so it's specific to this renderer.

Happy to open a PR for the .strip() if you'd like.

Environment

• sphinxcontrib-openapi 0.9.0
• sphinxcontrib-httpdomain 2.0.0
• Sphinx 8.2.3
• docutils 0.21.2
• Python 3.12.13

Start in sphinxcontrib/openapi/renderers/_httpdomain.py at the summary interpolation around line 284, then reproduce the issue with the provided spec.yml, index.rst, and conf.py. Run sphinx-build -W -b html src out and confirm the block-scalar summary renders as strong text without a warning or literal asterisks, while the existing plain-scalar behavior remains unchanged.