DOCS-229 Update PG Server page with PCI note (#896)

This PR updates the PG Server page with a PCI note and also improve paragraphs with proper links. It also removes that WAL is still in development.

Author: Andriciuc

docs/postgresql-server.md

@@ -1,12 +1,18 @@
 # Percona Server for PostgreSQL
 
-Percona Server for PostgreSQL is a binary-compatible, open source drop-in replacement for PostgreSQL 17. It introduces additional features to the upstream server, including:
+Percona Server for PostgreSQL is a binary-compatible, open source drop-in replacement for PostgreSQL 17. It introduces additional features on top of the upstream server, including:
 
-* Storage Manager (SMGR) API Exposure: Allows PostgreSQL extensions to integrate custom storage managers. This change was inspired by the [patchset](https://www.postgresql.org/message-id/flat/CAJ7c6TOqqrzjYsU6LgDkcJ0yVgzdkx2juJjgAjzP2jPOpZ1qUA%40mail.gmail.com#8e68cfc57fcac14c8e24b00b41e61baf) introduced to the community.
-* WAL Read/Write API Exposure to hook into WAL read and write functions.
+* Storage Manager (SMGR) API Exposure: Allows PostgreSQL extensions to integrate custom storage managers. This change was inspired by the [patchset :octicons-link-external-16:](https://www.postgresql.org/message-id/flat/CAJ7c6TOqqrzjYsU6LgDkcJ0yVgzdkx2juJjgAjzP2jPOpZ1qUA%40mail.gmail.com#8e68cfc57fcac14c8e24b00b41e61baf) introduced to the community.
+* WAL Read/Write API Exposure: Allows extensions to hook into WAL read and write functions.
 
-These modifications have no impact on existing use cases and operation of PostgreSQL. They are required to enable additional encryption capabilities such as index-level and Write-Ahead Logging (WAL) encryption of indexes through the [`pg_tde` :octicons-link-external-16:](https://docs.percona.com/pg-tde/index.html) extension. These encryption features provided by the `pg_tde` are still under active development and are planned for future releases.
+These changes do not affect existing use cases and PostgreSQL behavior. They enable additional encryption features, such as index-level and Write-Ahead Logging (WAL) encryption, through the [`pg_tde` :octicons-link-external-16:](https://docs.percona.com/pg-tde/index.html) extension.
 
-Percona Server and upstream PostgreSQL function identically enabling you to migrate from one to another. 
+Percona Server and the upstream PostgreSQL operate identically, making migrations between the two straightforward.
 
-[Get started :material-arrow-right:](installing.md){.md-button}
+[Get started :material-arrow-right:](installing.md){.md-button}
+
+!!! note
+
+    The PostgreSQL Compatibility Index [(PCI)](https://pgscorecard.com/) test suite reported **100% compatibility**. PCI validates behavioral equivalence by running a suite of compatibility checks against upstream PostgreSQL.
+
+    These results were obtained using [Percona Server for PostgreSQL 17.6.1 :octicons-link-external-16:](https://docs.percona.com/postgresql/17/index.html). [View the PCI test results here :octicons-link-external-16:](https://github.com/secp256k1-sha256/postgres-compatibility-index/blob/main/postgres-compatibility-index/outputs/Percona.json).