Add secure username/password login portal

Gate the suite behind a self-contained login (no external IdP):

- User model with bcrypt-hashed passwords; admin/user roles
- /api/auth endpoints: login, logout, me, change-password, and
  admin-only user management (list/create/delete/reset/enable)
- Stateless JWT session in an HttpOnly, SameSite=Lax, auto-Secure
  cookie; middleware refuses every /api data route without a session
- login.html + auth-guard.js: login page and per-page guard with a
  top-right "name / Admin / Sign out" pill
- Admin Console now gated on admin role (passphrase gate removed) with
  a User administration card
- manage_users.py CLI to bootstrap the first admin
- Rebuilt help.js into a searchable, multi-topic help center
- Local-dev convenience: app serves html/ so the site + API share one
  origin under uvicorn (inactive in the prod container)
- Docs/env: AUTH_SECRET_KEY, requirements (bcrypt, PyJWT), README

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

html/login.js

@@ -0,0 +1,59 @@
+/* Login page logic for the Work Package Suite.
+   Posts credentials to /api/auth/login. On success the server sets an HttpOnly
+   session cookie (not readable here — that's the point) and we redirect to the
+   page the user was trying to reach, or the home page. */
+(function () {
+  'use strict';
+
+  var form = document.getElementById('login-form');
+  var errorBox = document.getElementById('error');
+  var submitBtn = document.getElementById('submit');
+
+  // Where to go after signing in: the ?next= param if it's a safe same-site
+  // path, otherwise the home page. (Reject absolute/scheme URLs to avoid an
+  // open-redirect.)
+  function nextTarget() {
+    try {
+      var next = new URLSearchParams(location.search).get('next') || '';
+      if (next && next.charAt(0) === '/' && next.charAt(1) !== '/') return next;
+    } catch (e) {}
+    return 'index.html';
+  }
+
+  function showError(msg) {
+    errorBox.textContent = msg;
+    errorBox.classList.add('show');
+  }
+
+  form.addEventListener('submit', function (e) {
+    e.preventDefault();
+    errorBox.classList.remove('show');
+    var username = document.getElementById('username').value.trim();
+    var password = document.getElementById('password').value;
+    if (!username || !password) { showError('Enter your username and password.'); return; }
+
+    submitBtn.disabled = true;
+    submitBtn.textContent = 'Signing in…';
+
+    fetch('/api/auth/login', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ username: username, password: password })
+    })
+      .then(function (r) {
+        if (r.ok) { location.replace(nextTarget()); return null; }
+        return r.json().catch(function () { return null; }).then(function (j) {
+          if (r.status === 401) showError('Invalid username or password.');
+          else if (r.status === 403) showError((j && j.detail) || 'Your account is disabled.');
+          else showError((j && j.detail) || ('Sign-in failed (HTTP ' + r.status + ').'));
+          submitBtn.disabled = false;
+          submitBtn.textContent = 'Sign in';
+        });
+      })
+      .catch(function () {
+        showError('Could not reach the server. Check your connection and try again.');
+        submitBtn.disabled = false;
+        submitBtn.textContent = 'Sign in';
+      });
+  });
+})();