docs: contributor FAQ (Windows, grep -E, init frontmatter)

[tapheret2]

Summary

Adds docs/contributor-faq.md covering Windows path/slug casing, grep -E stripping vs ripgrep, and init frontmatter fields.

Closes #2922
Closes #2923
Closes #2924

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[tapheret2]

Contributor FAQ for Windows paths, grep -E stripping, and init frontmatter — closes the three docs issues if the table matches current CLI flags.

[tapheret2]

Closing this docs-only PR to keep the queue focused on higher-signal code changes. Thanks for the time reviewing.