Intw26 file upload poc

[gavxue]

Notion ticket link

Build file upload POC

Implementation description

• Added a reusable UploadFile component with client-side file validation for PDF/JPEG/PNG, selected-file preview, and upload status/error feedback.
• Added GraphQL upload support via multipart FormData helper and a new createFirebaseFile mutation.
• Added a test page at /review/uploadFile to manually verify end-to-end upload behavior in the app UI.

Steps to test

1. Start the app (with associated backend PR [INTW26] File upload POC website-bp-be#129) and go to /review/uploadFile.
2. Select a valid file (PDF/JPEG/PNG) and click Upload File.
3. Confirm success message appears and the input resets after upload.
4. Try an invalid type (for example .txt) and confirm validation error appears.
5. (Optional) Simulate backend failure and confirm upload error state is shown.

What should reviewers focus on?

• GraphQL mutation
• File validation and UX states (idle/uploading/success/error), including edge cases.

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR