docs: explain required versioned regex input

[vjymisal0]

What changed

• Document that enable-versioned-regex is required, has no default, and fails when omitted.
• Explain when to use 0 versus 1, linking to the existing versioned-template example.
• Supply the required input in the title-only workflow example.

Why

Fixes #84. Existing examples demonstrate versioning but do not explicitly explain whether the input can be omitted.

Validation

• Parsed all five README action workflow examples and checked their versioning input.
• Offline checks against the actual TypeScript source with real @actions/core input handling and mocked GitHub/filesystem passed: omitted input, versioning disabled, versions 1 and 2, and missing version marker.
• node node_modules/typescript/bin/tsc --noEmit passed.
• Production ncc bundle build passed with output redirected outside tracked files.
• git diff --check passed.

Notes

Documentation only; no action behavior, dependencies, or generated bundle changes. The package test script is a failing placeholder and no lint script is defined. Validation harness and workflow records are local metadata, not part of this PR. No live GitHub Actions execution was performed.

Risks

Low: documents the existing required-input contract without changing it.

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