SUP-001: Help Center — searchable FAQ and article library

## Overview
Build a self-service Help Center with categorized articles and a search function. Articles cover common topics: shipping, returns, account, payments.

## Acceptance Criteria
- [ ] Help Center accessible from the footer and support nav
- [ ] Articles organized by category (Shipping, Returns, Account, Payments, Products)
- [ ] Search bar filters articles by keyword
- [ ] Article detail page with breadcrumb nav
- [ ] 'Was this helpful?' feedback on each article

## Notes
No upstream dependencies — can be built independently.

Start by inspecting the existing footer and support navigation entry points to determine where the Help Center should be linked. Map the article categories, search, article detail, breadcrumbs, and feedback requirements, then verify that each acceptance criterion is covered.

Written by the indexing model from the issue text.