feat: customer password reset via email round-trip (#32)

Adds "Forgot password?" to the login page, a request page, and a reset
page reached by a one-hour, single-use token delivered by email. Reuses
customer_tokens with a new password_reset kind alongside verify_email.

The request endpoint always answers 200, whether or not the address has
an account, so it cannot be used to test addresses for membership. Note
/register still reveals existence through its 409 on a duplicate, so this
protection is currently partial; closing that is its own change.

Completing a reset deletes every session for that customer. A reset
prompted by a compromise has to evict the intruder, and leaving a 30-day
cookie alive would defeat the point. It also marks the address verified,
since receiving the mail is exactly what verification proves, and
supersedes any outstanding token so an older link in the inbox cannot be
resurrected.

Introduces the first rate limiting in the codebase, on the request
endpoint only. The limiter is keyed on caller *and* submitted address:
keying on IP alone would let one person lock out everyone behind the same
proxy, and everything arrives via Nginx Proxy Manager. Applying that same
limiter to the reset endpoint, which carries no address, collapsed every
caller into one shared bucket -- so that endpoint is deliberately
unlimited instead, protected by a 32-byte single-use token whose bcrypt
work only runs after the token matches.

The e2e tests read the issued token directly from Postgres rather than
through a test-support endpoint. An endpoint returning a reset token for
an arbitrary address is account takeover for every customer if it is ever
reachable, and an environment gate is thin protection against that.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/package.json

@@ -19,30 +19,31 @@
     "migrate:create": "node-pg-migrate create --migration-file-language js"
   },
   "dependencies": {
-    "express": "^4.19.2",
-    "pg": "^8.12.0",
-    "multer": "^1.4.5-lts.1",
     "bcryptjs": "^2.4.3",
     "cookie-parser": "^1.4.6",
-    "nodemailer": "^6.9.14",
+    "express": "^4.19.2",
+    "express-rate-limit": "^8.6.2",
+    "multer": "^1.4.5-lts.1",
     "node-cron": "^3.0.3",
-    "node-pg-migrate": "^7.6.1"
+    "node-pg-migrate": "^7.6.1",
+    "nodemailer": "^6.9.14",
+    "pg": "^8.12.0"
   },
   "devDependencies": {
-    "typescript": "^5.5.4",
-    "tsx": "^4.16.5",
-    "@types/express": "^4.17.21",
-    "@types/node": "^20.14.15",
-    "@types/multer": "^1.4.11",
-    "@types/pg": "^8.11.6",
     "@types/bcryptjs": "^2.4.6",
     "@types/cookie-parser": "^1.4.7",
-    "@types/nodemailer": "^6.4.15",
-    "@types/node-cron": "^3.0.11",
-    "jest": "^29.7.0",
-    "ts-jest": "^29.2.4",
+    "@types/express": "^4.17.21",
     "@types/jest": "^29.5.12",
+    "@types/multer": "^1.4.11",
+    "@types/node": "^20.14.15",
+    "@types/node-cron": "^3.0.11",
+    "@types/nodemailer": "^6.4.15",
+    "@types/pg": "^8.11.6",
+    "@types/supertest": "^6.0.2",
+    "jest": "^29.7.0",
     "supertest": "^7.0.0",
-    "@types/supertest": "^6.0.2"
+    "ts-jest": "^29.2.4",
+    "tsx": "^4.16.5",
+    "typescript": "^5.5.4"
   }
-}
+}