feat: Azure (Entra ID) login as user login (#16)

Replaces the client-side PIN login with real authentication against Azure
Entra ID via PocketBase's built-in OAuth2 (OIDC) flow. Every Azure user is
auto-provisioned as a team_member on first login.

- pb_migrations: team_members becomes a PocketBase auth collection (OIDC
  provider configured from env); all collections require @request.auth.id
- pb_hooks: provisioning of role (ENTRA_ADMIN_EMAILS allow-list) and
  enrollment_status, with admin-role re-sync on every login
- frontend: "Sign in with Microsoft" login, pb.authStore-based session,
  TeamManager manages roster/roles (no PIN/manual create)
- infra: Entra env wiring + pb_hooks mount for dev (Labs) and prod
- src/lib/azureAuth.js + tests for the canonical role/allow-list logic
- docs/auth-spec.md

Knowledge base, generated tests and micro-learnings are left untouched.
Existing PIN users are dropped (no migration required, per sign-off).

Closes #16

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

scripts/setup-pb-collections.mjs

@@ -102,17 +102,21 @@ const COLLECTIONS = [
       ...AUTODATE_FIELDS,
     ],
   },
+  // NOTE: `team_members` is an AUTH collection owned by the migration
+  // pb_migrations/1781000000_team_members_to_auth.js (Azure/Entra ID login).
+  // Migrations run on PocketBase start — before this script — so the entry
+  // below is only a fallback for environments where migrations have not run;
+  // when the auth collection already exists, this create is skipped.
   {
     name: 'team_members',
-    type: 'base',
+    type: 'auth',
     ...OPEN_RULES,
+    passwordAuth: { enabled: false, identityFields: ['email'] },
     fields: [
-      { name: 'name', type: 'text', required: true },
-      { name: 'pin',  type: 'text', required: false },
+      { name: 'name', type: 'text', required: false },
       { name: 'role', type: 'text', required: false },
       { name: 'curriculum_started_at', type: 'date', required: false },
       { name: 'enrollment_status',     type: 'text', required: false },
-      ...AUTODATE_FIELDS,
     ],
   },
   {