Render bracket references as superscript text

This commit improves markdown rendering to convert reference labels
(e.g., `[1]`) to superscripts, improving document readability without
cluttering the text. This improvement applies documentation of all
scripts and categories.

Changes:

- Implement superscript conversion for reference labels within markdown
  content, ensuring a cleaner presentation of textual references.
- Enable HTML content within markdown, necessary for inserting `<sup>`
  elements due to limitations in `markdown-it`, see
  markdown-it/markdown-it#999 for details.
- Refactor markdown rendering process for improved testability and
  adherence to the Single Responsibility Principle.
- Create `_typography.scss` with font size definitions, facilitating
  better control over text presentation.
- Adjust external URL indicator icon sizing for consistency, aligning
  images with the top of the text to maintain a uniform appearence.
- Use normal font-size explicitly for documentation text to ensure
  consistency.
- Remove text size specification in `markdown-styles` mixin, using `1em`
  for spacing to simplify styling.
- Rename font sizing variables for clarity, distinguishing between
  absolute and relative units.
- Change `font-size-relative-smaller` to be `80%`, browser default for
  `font-size: smaller;` CSS style and use it with `<sup>` elements.
- Improve the logic for converting plain URLs to hyperlinks, removing
  trailing whitespace for cleaner link generation.
- Fix plain URL to hyperlink (autolinking) logic removing trailing
  whitespace from the original markdown content. This was revealed by
  tests after separating its logic.
- Increase test coverage with more tests.
- Add types for `markdown-it` through `@types/markdown-it` package for
  better editor support and maintainability.
- Simplify implementation of adding custom anchor attributes in
  `markdown-it` using latest documentation.

tests/unit/shared/Stubs/MarkdownRendererStub.ts

@@ -0,0 +1,31 @@
+import type { MarkdownRenderer } from '@/presentation/components/Scripts/View/Tree/NodeContent/Markdown/MarkdownRenderer';
+import { expectExists } from '@tests/shared/Assertions/ExpectExists';
+import { StubWithObservableMethodCalls } from './StubWithObservableMethodCalls';
+
+export class MarkdownRendererStub
+  extends StubWithObservableMethodCalls<MarkdownRenderer>
+  implements MarkdownRenderer {
+  private renderOutput = `[${MarkdownRendererStub.name}]render output`;
+
+  public render(markdownContent: string): string {
+    this.registerMethodCall({
+      methodName: 'render',
+      args: [markdownContent],
+    });
+    return this.renderOutput;
+  }
+
+  public withRenderOutput(renderOutput: string): this {
+    this.renderOutput = renderOutput;
+    return this;
+  }
+
+  public assertRenderWasCalledOnceWith(expectedInput: string): void {
+    const calls = this.callHistory.filter((c) => c.methodName === 'render');
+    expect(calls).to.have.lengthOf(1);
+    const [call] = calls;
+    expectExists(call);
+    const [actualInput] = call.args;
+    expect(actualInput).to.equal(expectedInput);
+  }
+}