fix(web): proxy RSS feed API requests

[technowizard]

Summary

• Add /feeds to the production nginx API proxy allowlist.
• Prevent RSS subscription requests from falling through to the SPA.
• Document the production fix under CHANGELOG.md → Unreleased.

Why

Production nginx was serving the web app for /feeds/* requests because the route prefix was omitted from the proxy location. GET requests returned index.html, while POST /feeds/subscriptions returned nginx 405 Not Allowed. Local development bypassed nginx through the Vite API configuration, so the issue only appeared in production.

Verification

• Reproduced the production 405 before the fix.
• Rendered the template with the production nginx:alpine image and passed nginx -t.
• Confirmed the rendered API proxy location includes feeds.
• git diff --check passed.
• CHANGELOG.md formatting passed.

Risk

This changes only the web container's nginx route allowlist; no application API behavior changes.