[paulyhedral]

Summary

• Embed shared-web feedback widget in nav #247 set the feedback widget's data-api-url to https://api.admin.dev.sweetrpg.com/api/0/feedback - a host that doesn't exist on this platform
• admin-api is exposed under the same dev.sweetrpg.com host as main-web, at /api/0/admin/<route> (see docs/deployment-conventions.md's "API Ingress path versioning"), so this call is same-origin, not cross-origin
• Fix FEEDBACK_API_URL's default to the correct path-only value: /api/0/admin/feedback

Confirmed against the live dev endpoint:

• https://api.admin.dev.sweetrpg.com/... -> 404 (host doesn't route anywhere meaningful)
• https://dev.sweetrpg.com/api/0/admin/feedback -> 200 {"status":"accepted"}

(The ALLOWED_ORIGINS CORS config added to admin-api in sweetrpg/admin-api#95 turns out to be unnecessary - same-origin requests don't need CORS - but it's harmless to leave in place.)

Test plan

• cargo fmt --check, cargo clippy --all-targets, cargo test pass
• Manual dev-environment check: submit via the widget, confirm 200 and a real GitHub issue lands on sweetrpg/platform