Sanitize no-break whitespace (U+00A0) in frontmatter before YAML parsing

[Copilot]

• Add sanitization of no-break whitespace (U+00A0) in frontmatter YAML before parsing in pkg/parser/frontmatter_content.go
• Add test cases to pkg/parser/frontmatter_extraction_test.go for no-break whitespace handling
• Run make fmt, make lint, make build to validate changes

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[Copilot]

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[pelikhan]

@copilot create helper function to parse YAML that always applies the space normalization.

[pelikhan]

Regression test:

---
on:
  workflow_dispatch:
permissions:
  issues: read
  contents: read
tools:
  github:
    toolsets: [default, actions]
  bash: true
safe-outputs:
  github-token: ${{ secrets.GITHUB_TOKEN }}
  create-issue:
  update-issue:
    body:
    footer: false
    target: "*"
    target-repo: "*"
    max: 5
---

Testing.