feat: add PostgreSQL MCP server definition

Add community PostgreSQL MCP server using @modelcontextprotocol/server-postgres.
Read-only SQL access with connection URL input.

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

servers/community.postgresql.json

@@ -0,0 +1,55 @@
+{
+  "$schema": "../schemas/server-definition.schema.json",
+  "id": "community.postgresql",
+  "name": "PostgreSQL",
+  "alias": "postgres",
+  "description": "Query PostgreSQL databases with read-only access. Execute SQL queries, inspect table schemas, and explore data in any PostgreSQL database.",
+  "icon": "https://avatars.githubusercontent.com/u/182288589?v=4",
+  "schema_version": "2.1",
+  "categories": ["database"],
+  "tags": ["postgres", "postgresql", "database", "sql", "query", "relational"],
+
+  "transport": {
+    "type": "stdio",
+    "command": "npx",
+    "args": ["-y", "@modelcontextprotocol/server-postgres", "${input:POSTGRES_URL}"],
+    "metadata": {
+      "inputs": [
+        {
+          "id": "POSTGRES_URL",
+          "label": "PostgreSQL Connection URL",
+          "description": "PostgreSQL connection string including host, port, database name, and credentials. All queries run in read-only transactions.",
+          "type": "password",
+          "required": true,
+          "secret": true,
+          "placeholder": "postgresql://username:password@localhost:5432/mydb"
+        }
+      ]
+    }
+  },
+
+  "auth": {
+    "type": "none"
+  },
+
+  "contributor": {
+    "name": "Model Context Protocol",
+    "github": "modelcontextprotocol",
+    "url": "https://modelcontextprotocol.io"
+  },
+
+  "links": {
+    "repository": "https://github.com/modelcontextprotocol/servers",
+    "homepage": "https://www.postgresql.org",
+    "documentation": "https://github.com/modelcontextprotocol/servers/tree/main/src/postgres#readme"
+  },
+
+  "platforms": ["all"],
+
+  "capabilities": {
+    "tools": true,
+    "resources": true,
+    "prompts": false,
+    "read_only_mode": true
+  }
+}