feat: SaaS onboarding, Stripe billing, MFA, SSO, passkeys, refresh tokens

Complete SaaS self-service onboarding sprint:

- Stripe-powered signup flow: pricing page → checkout → provisioning → activation
- Refresh token infrastructure: 1h access tokens + 30-day httpOnly cookie refresh
- TOTP MFA with QR setup, recovery codes, and login challenge flow
- Google + Azure AD SSO (conditional on env vars) with account linking
- WebAuthn passkey registration and passwordless login
- Guided onboarding checklist with server-side progress tracking
- Stubbed email service (console + DB logging, ready for real provider)
- Settings page with tabbed security settings (MFA, passkeys, linked accounts)
- Login page enhanced with MFA verification, SSO buttons, passkey login
- Database migration 015 with all new tables and columns
- Version bump to 2026.03.17

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "hoa-ledgeriq-frontend",
-  "version": "2026.03.10",
+  "version": "2026.3.11",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "hoa-ledgeriq-frontend",
-      "version": "2026.03.10",
+      "version": "2026.3.11",
       "dependencies": {
         "@mantine/core": "^7.15.3",
         "@mantine/dates": "^7.15.3",
@@ -14,6 +14,7 @@
         "@mantine/hooks": "^7.15.3",
         "@mantine/modals": "^7.15.3",
         "@mantine/notifications": "^7.15.3",
+        "@simplewebauthn/browser": "^13.3.0",
         "@tabler/icons-react": "^3.28.1",
         "@tanstack/react-query": "^5.64.2",
         "axios": "^1.7.9",
@@ -1289,6 +1290,12 @@
         "win32"
       ]
     },
+    "node_modules/@simplewebauthn/browser": {
+      "version": "13.3.0",
+      "resolved": "https://registry.npmjs.org/@simplewebauthn/browser/-/browser-13.3.0.tgz",
+      "integrity": "sha512-BE/UWv6FOToAdVk0EokzkqQQDOWtNydYlY6+OrmiZ5SCNmb41VehttboTetUM3T/fr6EAFYVXjz4My2wg230rQ==",
+      "license": "MIT"
+    },
     "node_modules/@tabler/icons": {
       "version": "3.36.1",
       "resolved": "https://registry.npmjs.org/@tabler/icons/-/icons-3.36.1.tgz",