docs: --local supports git library inputs

[Ryan-Amirthan]

Summary

fern-api/fern#17510 (CLI 5.103.0) removed the restriction that fern docs md generate --local only accepted path library inputs. git inputs are now parsed locally too, at the configured ref and honoring subpath.

Docs changes:

• Library Reference: the input tabs are no longer labeled "(remote)"/"(local)", and the generate-step tabs are re-cut by where parsing happens rather than by input type.
• Config reference: input.git works with --local; input.ref documented as branch, tag, or commit SHA; the C++ Doxyfile note now resolves paths against the source root (input.path, or the repository root for a git input) instead of always input.path.
• CLI reference fern docs md generate --local description updated to match.
• New Docs changelog entry for 2026-08-24.

Link to Devin session: https://app.devin.ai/sessions/8a2ce83d060e4ee185798aec35b2d36d
Requested by: @Ryan-Amirthan

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1787614438-local-library-git-inputs.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/cli-api-reference/cli-reference/docs-commands
• learn/docs/api-references/library-reference
• learn/docs/changelog/2026/8/24

[github-actions]

📝 [vale] <FernStyles.Hedges> _{reported by reviewdog 🐶}
Avoid hedge words and filler like 'just'. Prefer direct statements.