Architecture Cleanup: Fix Post Extension Mismatch (.md vs .markdown)

[JMG3000]

Jira Tracking

• Jira Site: https://jmg-github-revamp.atlassian.net
• Jira Project: PIMP
• Jira Issue Type: Task
• Jira Key: PIMP-8
• Jira Priority: Highest
• Jira URL: https://jmg-github-revamp.atlassian.net/browse/PIMP-8

Objective

Standardize blog post file extension handling.

Scope

• Update config/site.ts reader to support .markdown (or rename files to .md)
• Keep a single extension convention in content/posts

Acceptance Criteria

• A sample post in content/posts loads without path errors
• Extension convention is documented and consistently used