Adds the 'Oracle-to-PostgreSQL Migration Expert' Custom Agent, Asociated Skills, and Plugin Manifest (#950)

* Add the 'Oracle-to-PostgreSQL Migration Expert' Custom Agent, its associated skills, plugin manifest

* Update READMEs using 'npm run build'

* Resolve PR comments:
- Fix BOM characters
- Rerun 'npm run build'
- Clarify timestampz date kind
- Remove consufing text for SELECT INTO exception
- Remove dangerous VB.NET example

* Update README and refcursor handling documentation for clarity and consistency

* Update skills/creating-oracle-to-postgres-master-migration-plan/SKILL.md

Add .slnx to discovery of projects

Co-authored-by: Aaron Powell <me@aaron-powell.com>

---------

Co-authored-by: TCPrimedPaul <paul.delannoy@tc.gc.ca>
Co-authored-by: Aaron Powell <me@aaron-powell.com>

.github/plugin/marketplace.json

@@ -209,6 +209,12 @@
       "description": "Generate production-ready FastAPI applications from OpenAPI specifications. Includes project scaffolding, route generation, dependency injection, and Python best practices for async APIs.",
       "version": "1.0.0"
     },
+    {
+      "name": "oracle-to-postgres-migration-expert",
+      "source": "oracle-to-postgres-migration-expert",
+      "description": "Expert agent for Oracle-to-PostgreSQL application migrations in .NET solutions. Performs code edits, runs commands, and invokes extension tools to migrate .NET/Oracle data access patterns to PostgreSQL.",
+      "version": "1.0.0"
+    },
     {
       "name": "ospo-sponsorship",
       "source": "ospo-sponsorship",