Migrate PR conversations data to hierarchical chunking (XXxx)

Context

Per the Epic #11120, we are applying the hierarchical chunking (XXxx/) storage pattern to GitHub content directories. The code enablement for PR conversations has been handled in #11117.

The Problem

The resources/content/pulls/ directory holds over 700 files and is approaching the 1,000-file GitHub ceiling. If we don't migrate the data, future syncs will fail. We are separating this data migration from the code logic (per #11116) to prevent massive file-move diffs from obscuring logic review.

The Architectural Reality

The chunking algorithm (id.slice(0, -2) + 'xx') natively distributes these files into 100-file increments without breaking ingestion paths, now that the underlying code supports it.

The Fix

• Physically move all .md files currently in resources/content/pulls/ and its corresponding archive into the newly required XXxx/ nested directory structure.

Acceptance Criteria

• 100% of PR conversation markdown files are located in XXxx subdirectories.
• No flat .md files remain at the root of resources/content/pulls/ (excluding index/readme files if any).
• Data-only PR is opened and cleanly passes review without logic changes.