feat: Allow serving blog posts as markdown

[linkdotnet]

No description provided.

[Copilot]

🟡 Changes recommended

Content negotiation can return HTML despite an explicit rejection because wildcard quality overrides a more specific media range.

1 open issue

• Resolve HTML quality by specific Accept media range · New

What changed in this PR

Adds optional Markdown responses for published blog posts alongside the existing HTML pages.

Changes:

• Introduces content negotiation and Markdown rendering with metadata and expanded short codes.
• Adds a disabled-by-default setting and configuration migration to version 17.0.
• Adds tests and setup documentation.

File	Description
tools/​LinkDotNet.Blog.UpgradeAssistant/​Migrations/​Migration_16_To_17.cs	Adds the disabled setting.
tools/​LinkDotNet.Blog.UpgradeAssistant/​MigrationDiscovery.cs	Registers the migration.
tests/​LinkDotNet.Blog.UpgradeAssistant.Tests/​MigrationManagerTests.cs	Tests upgrades to version 17.0.
tests/​LinkDotNet.Blog.UpgradeAssistant.Tests/​Migration16To17Tests.cs	Tests setting migration behavior.
tests/​LinkDotNet.Blog.UnitTests/​Web/​Features/​ShowBlogPost/​BlogPostMarkdownRendererTests.cs	Tests Markdown formatting and metadata.
tests/​LinkDotNet.Blog.UnitTests/​Web/​Features/​ShowBlogPost/​BlogPostMarkdownMiddlewareTests.cs	Tests content negotiation.
tests/​LinkDotNet.Blog.UnitTests/​Web/​Features/​MarkdownConverterTests.cs	Tests short-code expansion.
tests/​LinkDotNet.Blog.UnitTests/​Web/​ApplicationConfigurationTests.cs	Tests setting binding and default.
tests/​LinkDotNet.Blog.TestUtilities/​ApplicationConfigurationBuilder.cs	Supports the setting in test fixtures.
tests/​LinkDotNet.Blog.IntegrationTests/​BlogPostMarkdownTests.cs	Tests Markdown responses and HTML fallback.
src/​LinkDotNet.Blog.Web/​WebApplicationExtensions.cs	Conditionally enables middleware.
src/​LinkDotNet.Blog.Web/​Program.cs	Integrates middleware into the pipeline.
src/​LinkDotNet.Blog.Web/​Features/​ShowBlogPost/​ShowBlogPostPage.razor	Reuses shared short-code expansion.
src/​LinkDotNet.Blog.Web/​Features/​ShowBlogPost/​BlogPostMarkdownRenderer.cs	Renders Markdown with front matter.
src/​LinkDotNet.Blog.Web/​Features/​ShowBlogPost/​BlogPostMarkdownMiddleware.cs	Negotiates and serves published posts.
src/​LinkDotNet.Blog.Web/​Features/​MarkdownConverter.cs	Extracts shared short-code expansion.
src/​LinkDotNet.Blog.Web/​appsettings.json	Updates configuration version and default.
src/​LinkDotNet.Blog.Web/​ApplicationConfiguration.cs	Defines the feature setting.
MIGRATION.md	Documents the configuration upgrade.
docs/​Setup/​Configuration.md	Explains Markdown requests and responses.
docs/​Migrations/​UpgradeAssistant.md	Documents the new migration.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Plain-text titles need escaping to preserve their displayed content in Markdown headings.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Escape Markdown and HTML metacharacters in heading titles

src/​LinkDotNet.Blog.Web/​Features/​ShowBlogPost/​BlogPostMarkdownRenderer.cs:33

The title is plain text, but this line inserts it as Markdown syntax. For example, Understanding List<T> produces a heading whose <T> is treated as an HTML tag by Markdown renderers, so the displayed title loses the type argument. Escape Markdown/HTML metacharacters in the heading title while leaving the post body unchanged. Add a generic-type title regression test and update the existing assertion that expects an unescaped title backslash.

1 resolved since last review

• Resolve HTML quality by specific Accept media range

_{Review effort: Balanced}