[DOCS] Add GeoPandas API coverage reference

[jiayuasu]

Did you read the Contributor Guide?

Yes, I have read the Contributor Rules and Contributor Development Guide.

Is this PR related to a ticket?

Documentation update related to #2230; it does not close the implementation epic.

What changes were proposed in this PR?

Add a SedonaSpark GeoPandas API coverage reference, a coverage badge alongside the existing README badges, and a linked README summary so users can see which APIs are implemented and where limitations remain.

The reference compares the 2.0.0 development implementation with the pinned GeoPandas 1.1.4 catalogs: 160 of 175 APIs (91.4%) are available or partially available, and 15 are unsupported. The summary and per-API tables use these two status categories, with limitations retained in the notes. The percentage measures named API availability, including partial implementations, rather than complete parameter, semantic, or distributed-execution parity.

The page includes per-API limitations, category totals, counting rules, and maintenance guidance. All API links are pinned to GeoPandas 1.1.4. It is linked from the English and Chinese SedonaSpark navigation, landing pages, and GeoPandas guides, as well as the README; the Chinese coverage page uses the English fallback. The README badge carries the percentage, while its feature bullet links to the detailed reference. This is a documentation-only change.

How was this patch tested?

• Reconciled all 175 unique entries against the five pinned upstream catalogs, with no omissions or duplicates; verified category totals, the README percentage, and documentation links.
• Verified all 175 versioned API URLs return HTTP 200 without redirects outside the pinned version.
• Ran Markdown lint on all changed Markdown files and git diff --check.
• Built the English and Chinese documentation with mkdocs build; existing warnings concern generated API docs and unrelated site links. Verified both rendered coverage pages contain the final counts and 175 API rows.
• Used focused local probes to confirm the documented spatial-index and spatial-join limitations, including rectangle-clipping behavior across GeoSeries, GeoDataFrame, and the module-level API. An isolated source-level probe also confirmed that read_parquet silently ignores its four named options and warns for extra keyword arguments.

Did this PR include necessary documentation updates?

Yes. All changes are documentation updates.