feat(auth): wire lockout, rate-limit, and constant-time login into both routes

Both POST /login (HTML form) and POST /api/v1/auth/login now flow through
the shared attemptLogin() handler. Locked accounts respond with 401 +
Retry-After (generic body "Invalid credentials" / "Invalid username or
password") so attackers can't use lockout state as a username-existence
oracle.

@fastify/rate-limit registered with global=false; only the two login
routes opt in via per-route rateLimit config. File uploads and downloads
keep full throughput. Custom errorResponseBuilder logs AUTH_RATE_LIMITED
fire-and-forget so fail2ban can pick it up.

createTestApp now accepts Partial<Config> overrides so integration tests
can dial thresholds down without env-var mutation.

src/routes/pages.ts

@@ -6,10 +6,10 @@ import type Database from 'better-sqlite3';
 import type { Config } from '../config.ts';
 import type { Logger } from '../middleware/logging.ts';
 import type { JwtPayload } from '../types.ts';
-import { getUserByUsername } from '../db/users.ts';
+import type { LockoutService } from '../services/lockout.ts';
 import { createFile, getFileById, getFilesByUserId, deleteFile } from '../db/files.ts';
-import { verifyPassword } from '../services/auth.ts';
 import { saveFile, deleteStoredFile, getFilePath } from '../services/storage.ts';
+import { attemptLogin } from '../services/login-handler.ts';
 import { requireAuth, tokenCookieOptions } from '../middleware/auth.ts';
 import { loginPage } from '../views/login.ts';
 import { uploadPage, uploadResultPage } from '../views/upload.ts';
@@ -21,6 +21,7 @@ interface Deps {
   db: Database.Database;
   config: Config;
   logger: Logger;
+  lockout: LockoutService;
 }
 
 function parseRangeHeader(header: string, fileSize: number): { start: number; end: number } | null {
@@ -48,6 +49,12 @@ function parseRangeHeader(header: string, fileSize: number): { start: number; en
 
 export const pageRoutes: FastifyPluginAsync<{ deps: Deps }> = async (app, { deps }) => {
   const { db, config, logger } = deps;
+  const loginRateLimit = {
+    rateLimit: {
+      max: config.loginRateLimitMax,
+      timeWindow: config.loginRateLimitWindowSeconds * 1000,
+    },
+  };
 
   // GET / — login page or redirect if authed
   app.get('/', async (request, reply) => {
@@ -60,24 +67,37 @@ export const pageRoutes: FastifyPluginAsync<{ deps: Deps }> = async (app, { deps
   });
 
   // POST /login — form login
-  app.post<{ Body: { username?: string; password?: string } }>('/login', async (request, reply) => {
-    const { username = '', password = '' } = request.body ?? {};
-    const ip = request.ip;
-    const userAgent = request.headers['user-agent'] ?? '';
+  app.post<{ Body: { username?: string; password?: string } }>(
+    '/login',
+    { config: loginRateLimit },
+    async (request, reply) => {
+      const { username = '', password = '' } = request.body ?? {};
 
-    const user = getUserByUsername(db, username);
-    const valid = user ? await verifyPassword(password, user.password_hash) : false;
+      const result = await attemptLogin(deps, {
+        username,
+        password,
+        ip: request.ip,
+        userAgent: request.headers['user-agent'] ?? '',
+      });
 
-    if (!user || !valid) {
-      await logger.authFailure({ ip, userAgent, username });
-      return reply.type('text/html').send(loginPage({ error: 'Invalid username or password' }));
-    }
+      if (result.kind === 'locked') {
+        return reply
+          .type('text/html')
+          .header('Retry-After', String(result.retryAfterSeconds))
+          .send(loginPage({ error: 'Invalid username or password' }));
+      }
 
-    await logger.authSuccess({ ip, userAgent, username });
+      if (result.kind !== 'success') {
+        return reply.type('text/html').send(loginPage({ error: 'Invalid username or password' }));
+      }
 
-    const token = app.jwt.sign({ sub: user.id, username: user.username }, { expiresIn: config.jwtExpiry });
-    reply.setCookie('token', token, tokenCookieOptions(config.cookieSecure)).redirect('/upload');
-  });
+      const token = app.jwt.sign(
+        { sub: result.user.id, username: result.user.username },
+        { expiresIn: config.jwtExpiry },
+      );
+      reply.setCookie('token', token, tokenCookieOptions(config.cookieSecure)).redirect('/upload');
+    },
+  );
 
   // POST /logout
   app.post('/logout', { preHandler: requireAuth }, async (_request, reply) => {