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>

pb_migrations/1781000001_tighten_api_rules.js

@@ -0,0 +1,57 @@
+/// <reference path="../pb_data/types.d.ts" />
+//
+// Issue #16 — Lock down API rules now that authentication is real.
+//
+// Before Azure login the app had no real auth, so every collection rule was
+// "" (public). With mandatory Entra OIDC login, every legitimate caller is
+// authenticated, so we require `@request.auth.id != ""` on all non-system,
+// non-`team_members` collections.
+//
+// This intentionally does NOT delete or restructure any data — it only changes
+// access rules. The knowledge base, generated tests and micro-learnings stay
+// exactly as they are; they simply become unreadable to anonymous callers.
+//
+// `team_members` is configured by its own migration (1781000000) and skipped
+// here. System collections (`_superusers`, `_mfas`, `_otps`, …) are skipped.
+//
+// NOTE (follow-up): for least-privilege we could further restrict write/delete
+// on the knowledge-authoring collections (topics, relations, content, sources,
+// question_bank, curriculum_versions) to `@request.auth.role = "admin"`. That
+// is deferred because micro_learnings / theme_sessions are written by regular
+// users (generate-then-cache) and the full matrix needs runtime verification.
+// The trust boundary today is: perimeter Azure gate + authenticated employees.
+const AUTHED = '@request.auth.id != ""';
+
+migrate((app) => {
+  const collections = app.findAllCollections();
+  for (const c of collections) {
+    if (c.system) continue;
+    if (c.name === "team_members") continue;
+
+    c.viewRule = AUTHED;
+    c.listRule = AUTHED;
+    // View collections only support list/view rules.
+    if (c.type !== "view") {
+      c.createRule = AUTHED;
+      c.updateRule = AUTHED;
+      c.deleteRule = AUTHED;
+    }
+    app.save(c);
+  }
+}, (app) => {
+  // Down: restore fully public rules (the pre-Azure baseline).
+  const collections = app.findAllCollections();
+  for (const c of collections) {
+    if (c.system) continue;
+    if (c.name === "team_members") continue;
+
+    c.viewRule = "";
+    c.listRule = "";
+    if (c.type !== "view") {
+      c.createRule = "";
+      c.updateRule = "";
+      c.deleteRule = "";
+    }
+    app.save(c);
+  }
+});