refactor: share upload filename parser

[CircleCrop]

Motivation

• Prevent divergent filename parsing logic between the scanner and UI by extracting a single pure parser for flat upload filename stems.
• Ensure consistent handling of common separators (spaced dash, dash, underscore, dot) so grouping, labels, and tests remain aligned.

Description

• Add apps/internal-site/components/web-uploader/filename-parser.ts that exports parseUploadFilenameStem(stem) returning { prefix, frame, variant } | null and supports spaced-dash, dash, underscore, and dot separators.
• Replace the ad-hoc FILENAME_RE use in source-scanner.ts with the shared parseUploadFilenameStem helper and remove the local regex.
• Add fullFrameTitleFromSourcePath(path) to web-upload-view-model.ts, which uses the shared parser to produce ${prefix} - ${frame} or fall back to the stem.
• Add tests: filename-parser.test.ts (unit tests for separators and missing variant) and small regression tests added/updated in source-scanner.test.ts and web-upload-view-model.test.ts to ensure consistent behavior across scanner and view-model.

Testing

• Ran the internal-site test suite (Vitest) for the changed files, with all tests passing (Test Files 39 passed, Tests 126 passed).
• Ran linting for @magic-compare/internal-site with no errors.
• Ran typechecking/build (next build) for @magic-compare/internal-site, which completed successfully.

---

Codex Task

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[CircleCrop]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

Reviewed commit: 333d39944a

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".