Refactor resolveContentFileFromId in generateSeoFiles.mjs for accurate content path resolution

The resolveContentFileFromId function within buildScripts/generateSeoFiles.mjs is responsible for mapping ids from learn/tree.json to actual content files on disk. The current implementation includes a nestedCandidates logic that attempts to find README or index files within directories corresponding to tree.json ids.

This nestedCandidates logic appears to be an incorrect assumption or a "hallucination" as the tree.json ids are designed to provide direct paths to content files (e.g., benefits/Effort should map to learn/benefits/Effort.md). The current approach can lead to incorrect file resolution or unnecessary complexity.

Acceptance Criteria:

1. Simplify resolveContentFileFromId: Remove the nestedCandidates logic from resolveContentFileFromId.
2. Direct Path Resolution: The function should directly resolve content file paths by combining LEARN_DIR, the id (split into segments), and iterating through SUPPORTED_DOC_EXTENSIONS.
3. Accurate Extension Handling: Ensure that the function correctly appends the appropriate file extension (e.g., .md, .json) to the id to find the corresponding content file.
4. Validation: Verify that all ids in learn/tree.json correctly resolve to their respective content files after the refactoring.