feat(auth): replace email/password registration with OAuth2 (Google + GitHub)

- New /auth/[provider] route: generates state cookie, redirects to provider
- New /auth/[provider]/callback: exchanges code, fetches profile, auto-creates
  or links account, sets auth cookie
- pocketbase.ts: add oauth_provider/oauth_id to User; new getUserByOAuth(),
  createOAuthUser(), linkOAuthToUser() helpers; loginUser() drops email_verified gate
- pb-init-v3.sh: add oauth_provider + oauth_id fields (schema + migration)
- docker-compose.yml: GOOGLE/GITHUB client ID/secret env vars (replaces SMTP vars)
- Login page: two OAuth buttons (Google, GitHub) — register form removed
- /verify-email route and email.ts removed (provider handles email verification)
- /api/auth/register returns 410 (OAuth-only from now on)

docker-compose.yml

@@ -267,13 +267,11 @@ services:
       PUBLIC_UMAMI_SCRIPT_URL: "${PUBLIC_UMAMI_SCRIPT_URL}"
       # GlitchTip client + server-side error tracking
       PUBLIC_GLITCHTIP_DSN: "${PUBLIC_GLITCHTIP_DSN}"
-      # Email verification (Resend SMTP — shared with Fider/GlitchTip)
-      SMTP_HOST: "${FIDER_SMTP_HOST}"
-      SMTP_PORT: "${FIDER_SMTP_PORT}"
-      SMTP_USER: "${FIDER_SMTP_USER}"
-      SMTP_PASSWORD: "${FIDER_SMTP_PASSWORD}"
-      SMTP_FROM: "noreply@libnovel.cc"
-      APP_URL: "${ORIGIN}"
+      # OAuth2 providers
+      GOOGLE_CLIENT_ID: "${GOOGLE_CLIENT_ID}"
+      GOOGLE_CLIENT_SECRET: "${GOOGLE_CLIENT_SECRET}"
+      GITHUB_CLIENT_ID: "${GITHUB_CLIENT_ID}"
+      GITHUB_CLIENT_SECRET: "${GITHUB_CLIENT_SECRET}"
     healthcheck:
       test: ["CMD", "wget", "-qO-", "http://127.0.0.1:3000/health"]
       interval: 15s