Migrate authentication to Better Auth

Replace the hand-rolled JWT auth with Better Auth 1.6.25 httpOnly cookie
sessions, validated against the database on every request so revocation,
bans and role changes take effect immediately.

Backend:
- betterAuth.ts wires the Drizzle adapter, magic links, Google sign-in and
  the admin plugin; auth-schema.ts maps Better Auth's models onto the
  existing `users` table so user IDs and their foreign keys survive intact.
- routes/auth.ts is gone; Better Auth serves the standard endpoints and
  authExt.ts carries the flows it doesn't cover.
- auth.ts shrinks to session resolution and helpers; sessions/revocation in
  dashboard.ts now read and delete `auth_sessions` rows directly.
- Schema adds the Better Auth core + admin columns (email_verified, image,
  banned, ban_reason, ban_expires), with migrations and tests.
- rateLimit.ts resolves client IPs spoof-resistantly: proxy headers are only
  honoured from loopback/RFC1918 peers plus TRUSTED_PROXIES.
- passwordPolicy.ts centralises password validation.
- Bump drizzle-orm, drizzle-kit and better-sqlite3 to versions compatible
  with Better Auth.

Frontend:
- auth-client.ts plus a reworked AuthContext and api/client.ts move to
  cookie-based sessions; no more bearer tokens in requests or middleware.

photo-api:
- Validate Better Auth session cookies against the shared auth_sessions
  table instead of verifying JWTs; JWT_SECRET is no longer needed for user
  auth, and PHOTO_VIEW_SECRET now signs gallery view tokens.

BETTER_AUTH_SECRET and BETTER_AUTH_URL are required in production; the
deprecated JWT_SECRET stays only as the photo-api view-token fallback.

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

backend/src/routes/authExt.ts

@@ -0,0 +1,96 @@
+import { Hono } from 'hono';
+import { zValidator } from '@hono/zod-validator';
+import { z } from 'zod';
+import { eq } from 'drizzle-orm';
+import { auth } from '../lib/betterAuth.js';
+import { validatePassword } from '../lib/passwordPolicy.js';
+import { db, dbGet, users } from '../db/index.js';
+import { getNow, toDbBool } from '../lib/utils.js';
+import { rateLimitMiddleware } from '../lib/rateLimit.js';
+
+// Custom auth flows that Better Auth doesn't provide out of the box. Mounted
+// at /api/auth-ext to avoid colliding with Better Auth's /api/auth/* handler.
+const authExtRateLimit = rateLimitMiddleware({ max: 20, windowMs: 15 * 60 * 1000, prefix: 'auth-ext' });
+
+const authExt = new Hono();
+
+const claimAccountSchema = z.object({
+  password: z.string().min(10, 'Password must be at least 10 characters'),
+});
+
+// Complete a progressive-account claim. The user arrives here already holding
+// a session established by the claim magic link; this endpoint deliberately
+// accepts accountStatus 'unclaimed' sessions (requireAuth would reject them)
+// and is the ONLY endpoint that does.
+authExt.post('/claim-account', authExtRateLimit, zValidator('json', claimAccountSchema), async (c) => {
+  const session = await auth.api.getSession({ headers: c.req.raw.headers });
+  if (!session?.user) {
+    return c.json({ error: 'Unauthorized. Please use the claim link from your email.' }, 401);
+  }
+
+  const user = session.user as any;
+  if (user.banned || user.accountStatus === 'suspended') {
+    return c.json({ error: 'Account is suspended. Please contact support.' }, 403);
+  }
+  if (user.isClaimed && user.accountStatus === 'active') {
+    return c.json({ error: 'Account is already claimed' }, 400);
+  }
+
+  const { password } = c.req.valid('json');
+  const passwordValidation = validatePassword(password);
+  if (!passwordValidation.valid) {
+    return c.json({ error: passwordValidation.error }, 400);
+  }
+
+  // Creates the credential account with the argon2id hash from lib/betterAuth.ts
+  await auth.api.setPassword({
+    body: { newPassword: password },
+    headers: c.req.raw.headers,
+  });
+
+  // The magic link click proved email ownership
+  await (db as any)
+    .update(users)
+    .set({
+      isClaimed: toDbBool(true),
+      accountStatus: 'active',
+      emailVerified: true,
+      updatedAt: getNow(),
+    })
+    .where(eq((users as any).id, user.id));
+
+  return c.json({
+    message: 'Account claimed successfully!',
+    user: {
+      id: user.id,
+      email: user.email,
+      name: user.name,
+      role: user.role,
+      isClaimed: true,
+      phone: user.phone ?? null,
+      rucNumber: user.rucNumber ?? null,
+      languagePreference: user.languagePreference ?? null,
+    },
+  });
+});
+
+// Whether an email belongs to an unclaimed account. Deliberate, rate-limited
+// exception to enumeration-safety, matching the legacy register/login UX that
+// surfaced "this account can be claimed".
+authExt.get('/claim-eligibility', authExtRateLimit, async (c) => {
+  const email = c.req.query('email');
+  if (!email || !z.string().email().safeParse(email).success) {
+    return c.json({ canClaim: false });
+  }
+
+  const user = await dbGet<any>(
+    (db as any).select().from(users).where(eq((users as any).email, email))
+  );
+
+  const canClaim = !!user && !user.banned && user.accountStatus !== 'suspended'
+    && (!user.isClaimed || user.accountStatus === 'unclaimed');
+
+  return c.json({ canClaim });
+});
+
+export default authExt;