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>

CLAUDE.md

@@ -127,6 +127,7 @@ when the PB binary starts.
 - `docs/generation-spec.md` — learning content + micro-learning generation
 - `docs/curriculum-spec.md` — 26-week per-user curriculum engine
 - `docs/r42-spec.md` — the R42 chatbot
+- `docs/auth-spec.md` — Azure (Entra ID) login: OIDC via PocketBase, provisioning, roles
 - `docs/frontend-spec.md` — screens, routing, onboarding
 - `docs/gamification-spec.md` — points, badges, leaderboard
 - `micro-learning-spec.md` — micro-learning learner experience