feat: add testing infrastructure — Vitest, Playwright, CI, git hooks

Add comprehensive testing covering 420 unit/handler tests across 24 Vitest
files, 9 Playwright E2E specs, accessibility scans, and visual regression.
Includes GitHub Actions CI, Husky pre-push hook, and TESTING.md docs.

tests/server/setup.js

@@ -11,7 +11,8 @@ import {
   defineEventHandler,
   readBody,
   getQuery,
-  getRouterParam
+  getRouterParam,
+  sendRedirect
 } from 'h3'
 
 // Register real h3 functions as globals so server code that relies on
@@ -28,7 +29,14 @@ vi.stubGlobal('defineEventHandler', defineEventHandler)
 vi.stubGlobal('readBody', readBody)
 vi.stubGlobal('getQuery', getQuery)
 vi.stubGlobal('getRouterParam', getRouterParam)
+vi.stubGlobal('sendRedirect', sendRedirect)
 
 vi.stubGlobal('useRuntimeConfig', () => ({
-  jwtSecret: 'test-jwt-secret'
+  jwtSecret: 'test-jwt-secret',
+  helcimApiToken: 'test-helcim-token'
 }))
+
+// Stubs for Nitro auto-imported server/utils (used by handlers that don't explicitly import them)
+vi.stubGlobal('requireAuth', vi.fn())
+vi.stubGlobal('requireAdmin', vi.fn())
+vi.stubGlobal('validateBody', vi.fn(async (event) => readBody(event)))