fix: preserve structured upload variants

[CircleCrop]

Motivation

• Structured VSEditor-style filenames include an explicit variant in the regex match and that explicit variant must never be overridden by directory-level variantOverride hints.
• Non-structured filenames may omit an explicit variant, so the existing fallback order should still allow directory hints to supply a variant before defaulting to output.

Description

• In parseCandidate the structured branch now uses structured.variant.trim().toLowerCase() and includes a short comment explaining that directory variantOverride must not replace the structured regex variant.
• Kept the ordinary filename branch fallback order as match.groups.variant ?? variantOverride ?? "output" so explicit filename variants still take precedence.
• Added the test preserves explicit rip and flt variants inside an after directory to apps/internal-site/components/web-uploader/source-scanner.test.ts to cover explicit structured variants inside a nested after directory.
• Modified files: apps/internal-site/components/web-uploader/source-scanner.ts and apps/internal-site/components/web-uploader/source-scanner.test.ts.

Testing

• Ran pnpm --filter @magic-compare/internal-site test -- source-scanner.test.ts and the internal-site test suite completed with all tests passing, including the updated source-scanner.test.ts.
• Ran pnpm --filter @magic-compare/internal-site lint and ESLint reported no errors.

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Codex Task

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