feat(cli): add line number reporting to YAML validation errors

[Ryan-Amirthan]

Description

Refs: Slack thread from @Ryan-Amirthan about difficulty locating YAML configuration errors

Adds line number reporting to YAML validation errors for docs.yml, product.yml, and version.yml files. Error messages now use a clean file:line: format that is clickable in VS Code, JetBrains, and other modern terminals.

Before:

[error] Invalid object at path $.navigation[1].variants[0].layout[2].contents[1]: does not match any allowed schema (has properties: page)
Did you mean to add 'path'? at /navigation/1/variants/0/layout/2/contents/1

After:

/path/to/docs.yml:42: Invalid object at path $.navigation[1].variants[0].layout[2].contents[1]: does not match any allowed schema (has properties: page)
Did you mean to add 'path'?

The file:line: format at the start of the message enables click-to-navigate in supported terminals.

Changes Made

• Added YamlSourceMap interface and helper functions to validateAgainstJsonSchema.ts for line number lookup
• Updated formatErrorMessageWithFilePath to use file:line: prefix format (removed redundant JSON path suffix)
• Modified loadDocsWorkspace.ts to create a source map when parsing YAML and pass it to validation
• Updated validateProductConfig.ts and validateVersionConfig.ts to accept optional source map parameter
• Updated DocsConfigFileAstNodeTypes interface to include absoluteFilepath and sourceMap for version/product files
• Added js-yaml-source-map dependency to workspace-loader and docs-validator packages
• Added version 3.31.0 entry to CLI versions.yml

Testing

• Unit tests added/updated
• Manual testing completed (lint checks pass)

Human Review Checklist

• Verify the file:line: prefix format is clear and clickable in VS Code terminal
• Check that the interface changes to DocsConfigFileAstNodeTypes (adding required absoluteFilepath and sourceMap fields) don't break existing code
• Verify source map lookup handles edge cases (JSON Pointer escaping with ~0 and ~1, missing properties falling back gracefully)
• Confirm error messages are still informative when line number cannot be resolved

---

Link to Devin run: https://app.devin.ai/sessions/7dac2f5c0b3e4c9aab5279a854f15db8
Requested by: @Ryan-Amirthan (ryanstep@buildwithfern.com)

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