Add Feedback domain module: public submission flow, admin CRUD, reporting (#7)

Co-authored-by: Patrick Müller <mail@pmueller.me>
Reviewed-on: #7
Co-authored-by: Patrick Mueller <patrick@mueller-patrick.tech>
Co-committed-by: Patrick Mueller <patrick@mueller-patrick.tech>

CLAUDE.md

@@ -18,7 +18,7 @@ npx jest test/some.test.ts
 
 ## Architecture
 
-Express.js REST API in TypeScript with a service-oriented layering. The sole domain is `Calendar`, which organises **events** and **users**.
+Express.js REST API in TypeScript with a service-oriented layering. Domains: `Calendar` (events, users) and `Feedback` (concert feedback forms, mounted at `/feedback`, backed by its own `FEEDBACK_DB` — see `src/models/feedback/`: public submission flow, admin CRUD, reporting, and a Salesforce newsletter-sync integration).
 
 **Request path:**
 1. `app.ts` mounts `Calendar.router.ts` at `/calendar`
@@ -53,6 +53,14 @@ DB_HOST=
 DB_USER=
 DB_PASSWORD=
 CALENDAR_DB=
+FEEDBACK_DB=
+FEEDBACK_IP_SALT=
+FEEDBACK_RATE_LIMIT_MAX=
+FEEDBACK_RATE_LIMIT_WINDOW_MIN=
+SALESFORCE_ENABLED=
+SALESFORCE_API_URL=
+SALESFORCE_CLIENT_ID=
+SALESFORCE_CLIENT_SECRET=
 EMAIL_HOST=
 EMAIL_USERNAME=
 EMAIL_PASSWORD=