fix: don't crash PocketBase when Entra secrets are absent (#16)

Configuring an enabled OAuth2 provider with empty clientId/clientSecret
fails collection validation, aborting the migration and preventing
PocketBase from starting (502 on every /api call). Attach the OIDC
provider only when ENTRA_CLIENT_ID and ENTRA_CLIENT_SECRET are present;
otherwise create the auth collection without a provider.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pb_migrations/1781000000_team_members_to_auth.js

@@ -28,6 +28,28 @@ migrate((app) => {
   }
 
   const tenant = $os.getenv("ENTRA_TENANT_ID") || "common";
+  const clientId = $os.getenv("ENTRA_CLIENT_ID");
+  const clientSecret = $os.getenv("ENTRA_CLIENT_SECRET");
+
+  // Only configure the OIDC provider when credentials are actually present.
+  // PocketBase rejects an enabled OAuth2 provider with an empty clientId /
+  // clientSecret, which would abort this migration and prevent PocketBase from
+  // starting at all (502 on every /api call). When the secrets are absent the
+  // collection is created without a provider; once the ENTRA_* secrets are set,
+  // configure the provider via the PocketBase admin UI
+  // (Settings → Auth providers → OIDC) or re-apply this migration.
+  const oidcProviders = (clientId && clientSecret) ? [
+    {
+      name: "oidc",
+      clientId: clientId,
+      clientSecret: clientSecret,
+      authURL:     "https://login.microsoftonline.com/" + tenant + "/oauth2/v2.0/authorize",
+      tokenURL:    "https://login.microsoftonline.com/" + tenant + "/oauth2/v2.0/token",
+      userInfoURL: "https://graph.microsoft.com/oidc/userinfo",
+      displayName: "Microsoft",
+      pkce: true,
+    },
+  ] : [];
 
   // 2. Recreate `team_members` as an auth collection (same name → all existing
   //    `user_id` references in test_results, on_demand_attempts,
@@ -56,7 +78,7 @@ migrate((app) => {
     mfa:          { enabled: false, duration: 600, rule: "" },
 
     oauth2: {
-      enabled: true,
+      enabled: oidcProviders.length > 0,
       // Map the OIDC userinfo claims onto our fields.
       mappedFields: {
         id: "",
@@ -64,18 +86,7 @@ migrate((app) => {
         username: "",
         avatarURL: "",
       },
-      providers: [
+      providers: oidcProviders,
-        {
-          name: "oidc",
-          clientId:     $os.getenv("ENTRA_CLIENT_ID"),
-          clientSecret: $os.getenv("ENTRA_CLIENT_SECRET"),
-          authURL:     "https://login.microsoftonline.com/" + tenant + "/oauth2/v2.0/authorize",
-          tokenURL:    "https://login.microsoftonline.com/" + tenant + "/oauth2/v2.0/token",
-          userInfoURL: "https://graph.microsoft.com/oidc/userinfo",
-          displayName: "Microsoft",
-          pkce: true,
-        },
-      ],
     },
 
     fields: [