Refresh documentation styling with Furo theme

[vlad-perevezentsev]

This PR proposes a refresh of dpnp documentation styling and layout by migrating to the furo theme and improving the overall API documentation appearance

• Replace sphinx_rtd_theme with furo
• Update documentation dependencies in pyproject.toml, building_docs.yml and base_build_docs.txt
• Redesign the landing page using sphinx-design cards
• Add custom CSS/JS for cleaner NumPy-style API formatting
• Improve tables, section headers, parameter formatting and function signatures

dpnp logo (dpnp.svg) will be added in the future

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• Have you added a test, reproducer or referred to an issue with a reproducer?
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• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[coveralls]

coverage: 78.073%. remained the same — update_dpnp_docs into master

[github-actions]

Array API standard conformance tests for dpnp=0.21.0dev2=py313h509198e_27 ran successfully.
Passed: 1355
Failed: 5
Skipped: 16

[antonwolfy]

The dark-mode blocks only override table colors. The hardcoded background-color: #f5f5f5 on dd p.rubric / .admonition-title (line 40) is not overridden in dark mode → light text on a near-white background = unreadable section headers and admonition titles.

An an option we can either add matching dark-mode overrides, or better, use furo CSS variables (e.g. --color-background-secondary) which auto-adapt and would let you delete the duplicated dark-mode block entirely.

[antonwolfy]

If the separator appears inside an HTML tag/attribute (e.g. a title= with an en dash), substring splits mid-tag and corrupts markup. Locating the boundary via textContent (or DOM walking) might be safer.

[antonwolfy]

@media (prefers-color-scheme: dark) table rules (lines 77–84) still apply if the OS is dark but the user toggles furo to light. Furo's own CSS gates these with body:not([data-theme="light"]).

[antonwolfy]

Thank you @vlad-perevezentsev, LGTM!