Portal sign-in with the Ecare office login

Ecare staff sign in with their office username and password, checked by
the Ecare sign-in service from the backend (AUTH_TOKEN_API_URL); a good
Ecare login still needs a Portal User. Service down = "try again
shortly", never a wrong password. /api/auth/login, me, logout; sign-in
tries limited per address. Users page: Ecare office login or Portal
password per user. Context.md: 27/10 runs, the login retry bug.
71 test files, 1239 tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/templates/signin.html

@@ -105,6 +105,7 @@
   </section>
   <section class="auth-form">
     <h2>Sign in</h2>
+    {% if ecare_on %}<p class="note">Ecare staff: your Ecare office username and password.</p>{% endif %}
     {% if error %}<div class="msg bad" role="alert">{{ error }}</div>{% endif %}
     {% if no_users %}<div class="msg bad">No Portal Users yet. On this PC run
       <code>python tools\add_portal_user.py</code> to add the first Admin.</div>{% endif %}
@@ -124,7 +125,8 @@
     </form>
     <p class="note rules">Signed out after {{ idle_minutes }} minutes idle.
       {{ lock_after }} wrong passwords lock the account for
-      {{ lock_minutes }} minutes. Forgot it? An Admin can reset it.</p>
+      {{ lock_minutes }} minutes. Forgot a Portal password? An Admin can
+      reset it.</p>
   </section>
 </div>
 {% endblock %}