Release 3.0.3: refresh GitHub presentation and interface media

[DavidVoitenko]

Changes

• Rewrite the English and Russian GitHub guides around the current eight-tab interface, accurate 150-entry catalog / 106 default feeds, installation choices, API and limitations.
• Redesign the GitHub Pages landing page and refresh its canonical, Open Graph and Twitter metadata.
• Replace the social preview, animated tour and 16 interface screenshots with captures from the current app using synthetic documentation data only.
• Keep scan target URLs visible and move idle bulk actions below the Results table so they do not cover proxy rows.
• Retry brief Windows file locks during export publication and make the gateway expiry fixture deterministic on Windows filesystems.
• Refresh the repository About description/topics and prepare release 3.0.3 so downloaded builds match the pictured UI.
• Upload the new social preview in GitHub repository settings.

Verification

• Full local suite: 3,719 tests, no failures (2 expected skips).
• Product wheel verification and source-product smoke test passed.
• Social preview is 1280×640 and under 1 MB; GIF is 960×600 and under 1 MB. All README and site image references resolve.
• Landing page rendered at 320, 390, 768 and 1440 px without horizontal overflow, broken images or JavaScript errors.
• GitHub CI is running across Linux, macOS and Windows.