fix: extra text from component rendering (14 en pages affected)

[jp-knj]

Problem

Integration pages show extra "Astro integration" text, editor setup shows "Official" label that baseline doesn't render.

Affected: ~14 en pages × 14 locales ≈ 196 pages total

Example

markflow: "This Astro integration enables rendering"
baseline: "This enables rendering"

Sample files: en/guides/integrations-guide/react, en/guides/integrations-guide/vue, en/editor-setup

Root Cause

Component slot rendering includes additional markup/text that Astro's MDX baseline strips or hides.