feat: implement deposition frontend — convention catalog, upload, and dashboard

[rorybyrne]

Implement the frontend pages for the deposition workflow. This is the UI counterpart to the backend work in #30.

Pages

1. Convention Catalog

Card grid of available conventions with title, description, field summary, and submission count. Click to view details.

2. Convention Detail

Full schema description + "Download Template" button. Shows all fields, their types, which are required, and which ontologies are referenced.

3. Deposition Upload

Drag-drop the filled spreadsheet (.xlsx) + data files. Server validates against schema and returns field-by-field, row-by-row results inline. Fix and re-upload.

4. Deposition Dashboard

List of user's depositions with status tracking (Draft → Submitted → In Review → Accepted/Rejected).

Dependencies

• feat: implement deposition upload workflow with semantics domain #30 (backend deposition workflow) — API must exist first
• feat: implement ORCiD OAuth authentication #50 (authentication) ✅
• feat: implement authorization with Gate hierarchy and repo decorators #56 (authorization) ✅

Acceptance Criteria

• Convention catalog displays available conventions
• Convention detail shows schema fields and allows template download
• Upload page accepts spreadsheet + files and displays validation results
• Dashboard shows user's depositions with current status
• Auth integration — only authenticated users can create depositions
• End-to-end flow works in browser: browse conventions → download template → upload filled spreadsheet + files → track status