Fix Sphinx docs rendering by repairing missing figure assets and references

[Copilot]

The documentation pages were rendering with broken/missing figures because the referenced image files under docs/_static/images/*.svg did not exist in the repo. This PR aligns figure references with versioned assets so pages render consistently.

• Root cause addressed

  • Replaced broken figure paths in:
    • docs/index.rst
    • docs/quickstart.rst
  • Paths now point to a tracked static asset instead of non-existent SVG files.

• Docs asset normalization

  • Added docs/_static/images/overall.png as the in-repo image source used by docs pages.
  • Updated .gitignore to allow versioning docs static PNG assets (!docs/_static/images/*.png).

• Content accuracy cleanup

  • Removed repeated quickstart figure blocks whose captions/alt-text implied specialized visuals that were not actually present, avoiding misleading documentation until dedicated assets are added.

.. figure:: _static/images/overall.png
   :alt: CORE pipeline overview
   :align: center
   :width: 100%