feat(auth): Google OAuth, sealed session and default-deny gating (T9)

Gate the app behind Google sign-in restricted to verified @theodo.com
identities, and record the real reporter on filed defects (F9).

- nuxt-auth-utils for sealed cookie sessions + the Google OAuth handler,
  mounted at /auth/google/callback to match the registered redirect URI.
- isAllowedGoogleUser re-derives the domain from Google's verified email;
  the spoofable `hd` claim is deliberately ignored (DESIGN T9).
- Default-deny: server middleware 401s unauthenticated /api calls (health
  and the session endpoint excepted); a global route middleware redirects
  unauthenticated page navigations to /login.
- getReporter() now reads the session email instead of the dev stub.
- Env contract moves to nuxt-auth-utils names (NUXT_SESSION_PASSWORD,
  NUXT_OAUTH_GOOGLE_*); .env.example, compose and README updated.

Unit-tested: domain check (incl. hd-spoof + look-alike) and public-path
matching. Live OAuth round-trip pending manual verification.

tests/auth.spec.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect } from 'vitest'
+import { isAllowedGoogleUser } from '../server/utils/allowedGoogleUser'
+import { isPublicApiPath } from '../server/utils/authPaths'
+
+// F9: access is restricted to verified @theodo.com identities. The Google
+// `hd` (hosted-domain) claim is NOT trusted on its own — we re-derive the
+// domain from the verified email server-side (DESIGN T9).
+describe('isAllowedGoogleUser', () => {
+  it('allows a verified @theodo.com email', () => {
+    expect(isAllowedGoogleUser({ email: 'jane@theodo.com', email_verified: true })).toBe(true)
+  })
+
+  it('denies a non-theodo verified email even when hd claims theodo.com', () => {
+    expect(
+      isAllowedGoogleUser({ email: 'attacker@gmail.com', email_verified: true, hd: 'theodo.com' }),
+    ).toBe(false)
+  })
+
+  it('denies a theodo email that Google has not verified', () => {
+    expect(isAllowedGoogleUser({ email: 'jane@theodo.com', email_verified: false })).toBe(false)
+  })
+
+  it('matches the domain case-insensitively', () => {
+    expect(isAllowedGoogleUser({ email: 'jane@Theodo.COM', email_verified: true })).toBe(true)
+  })
+
+  it('denies when the email is missing', () => {
+    expect(isAllowedGoogleUser({ email_verified: true, hd: 'theodo.com' })).toBe(false)
+  })
+
+  it('denies a look-alike domain that merely ends in theodo.com', () => {
+    expect(isAllowedGoogleUser({ email: 'eve@nottheodo.com', email_verified: true })).toBe(false)
+  })
+})
+
+describe('isPublicApiPath', () => {
+  it('treats the health check as public', () => {
+    expect(isPublicApiPath('/api/health')).toBe(true)
+  })
+
+  it('treats the session endpoint as public', () => {
+    expect(isPublicApiPath('/api/_auth/session')).toBe(true)
+  })
+
+  it('gates the defects API', () => {
+    expect(isPublicApiPath('/api/defects')).toBe(false)
+  })
+
+  it('ignores the query string when matching', () => {
+    expect(isPublicApiPath('/api/health?probe=1')).toBe(true)
+  })
+})