docs: flatten content script UI options

[dvd233]

Overview

The factory-specific options pages currently render as ContentScriptUiOptions<T> & object, so shared options—especially append—are still hidden behind another API page after #2497.

• Render the integrated, iframe, and shadow-root option aliases as TypeDoc interfaces so shared and factory-specific properties appear together.
• Keep every positioning key present on each discriminated-union branch with optional never fields. This lets TypeDoc retain zIndex and alignment without accepting unsupported position/option combinations.
• Inherit the shared options summary and correct the alignment docs to reference position: "overlay".
• Redirect the previous type-alias URLs to the new interface pages so existing links keep working.

The generated pages now expose all 8 integrated, 9 iframe, and 12 shadow-root options directly. TypeDoc 0.25 emits its generic union-to-interface warning for these aliases, so I also verified the generated Markdown and rendered HTML to ensure no properties are discarded.

Manual Testing

• bun run check
• bun run docs:build
• Type-checked valid inline/overlay/modal configurations and invalid inline zIndex / modal alignment configurations.
• Asserted the complete property set in all three generated Markdown pages and their rendered HTML output.
• Verified the legacy URL redirects are included in the built site.

Related Issue

Closes #1452

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