Add shared scanner contract aliases

[alyldas]

Summary

• Add short shared scanner contract aliases: ScanInput, ScanHints, and ScanResult.
• Export the aliases from the public package entrypoint while keeping existing longer contract names.
• Document the aliases in the README and add compile-time coverage for the shared scanner shapes.

Validation

• npm ci
• npm run check with a temporary npm cache because the local user cache has permission-owned files
• npm pack --dry-run with a temporary npm cache

Benchmark Evidence

• No runtime benchmark is applicable for this PR because the change is type-only and does not alter scanner runtime behavior.
• Existing scanner check/scan/censor tests pass through npm run check.

Compatibility Notes

• Backward compatible additive public type exports only.
• Existing PreparedText, TextHints, and TextRangePipelineScanResult names remain supported.

Closes #38

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feat: add shared scanner contract aliases
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