Add Feedback domain module: public submission flow, admin CRUD, reporting

New /feedback API domain backed by its own FEEDBACK_DB, mirroring the
Calendar domain's router -> service -> DB pool layering:

- Public endpoints (no auth): eligible-events listing, event config,
  submission with honeypot + rate limiting (in-memory + DB backstop).
- Admin endpoints (session-header auth, reusing Calendar's users/sessions
  via a swappable feedback.auth.ts boundary): events/songs/questions CRUD,
  bulk reorder/assignment, aggregated reporting, CSV export.
- Schema in sql/feedback/001_init.sql (8 tables), applied and verified
  against the real FEEDBACK_DB.
- 64 Jest tests covering validation, auth, rate limiting, CSV escaping,
  and report aggregation (pure functions, no DB needed).

Includes fixes from a security review: path traversal defense doesn't
apply here (that's the frontend proxy, separate repo), but the
rate-limiter cluster does - recordSubmission now counts every processed
request (not just successful ones), the in-memory Map evicts empty
entries instead of growing unbounded, FEEDBACK_IP_SALT is required at
boot instead of silently degrading to unsalted hashing, and submission
answer/rating arrays are capped and de-duplicated to bound insert
amplification.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/feedback/ratelimit.test.ts

@@ -0,0 +1,20 @@
+import {hashIp} from '../../src/models/feedback/feedback.ratelimit';
+
+describe('hashIp', () => {
+	it('never returns the raw IP', () => {
+		const hash = hashIp('203.0.113.42');
+		expect(hash).not.toContain('203.0.113.42');
+	});
+
+	it('is deterministic for the same input', () => {
+		expect(hashIp('203.0.113.42')).toBe(hashIp('203.0.113.42'));
+	});
+
+	it('differs for different inputs', () => {
+		expect(hashIp('203.0.113.42')).not.toBe(hashIp('203.0.113.43'));
+	});
+
+	it('is a 64-char hex SHA-256 digest', () => {
+		expect(hashIp('203.0.113.42')).toMatch(/^[0-9a-f]{64}$/);
+	});
+});