v4.0.2: Add Web UI authentication and optional HTTPS

- Add single-admin login with SQLite3 user storage
- First-run setup wizard for admin account creation
- Account management page for password changes
- Optional HTTPS with auto-generated self-signed certificates
- Configurable via STEGASOO_AUTH_ENABLED, STEGASOO_HTTPS_ENABLED env vars
- UI improvements: larger QR previews, consistent panel styling
- Update docker-compose.yml with auth config and persistent volumes
- Update all documentation for v4.0.2

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/templates/login.html

@@ -0,0 +1,61 @@
+{% extends "base.html" %}
+
+{% block title %}Login - Stegasoo{% endblock %}
+
+{% block content %}
+<div class="row justify-content-center">
+    <div class="col-md-5 col-lg-4">
+        <div class="card">
+            <div class="card-header text-center">
+                <i class="bi bi-shield-lock fs-1 d-block mb-2"></i>
+                <h5 class="mb-0">Login</h5>
+            </div>
+            <div class="card-body">
+                <form method="POST" action="{{ url_for('login') }}">
+                    <div class="mb-3">
+                        <label class="form-label">
+                            <i class="bi bi-person me-1"></i> Username
+                        </label>
+                        <input type="text" name="username" class="form-control"
+                               value="{{ username }}" readonly>
+                    </div>
+
+                    <div class="mb-4">
+                        <label class="form-label">
+                            <i class="bi bi-key me-1"></i> Password
+                        </label>
+                        <div class="input-group">
+                            <input type="password" name="password" class="form-control"
+                                   id="passwordInput" required autofocus>
+                            <button class="btn btn-outline-secondary" type="button"
+                                    onclick="togglePassword('passwordInput', this)">
+                                <i class="bi bi-eye"></i>
+                            </button>
+                        </div>
+                    </div>
+
+                    <button type="submit" class="btn btn-primary w-100">
+                        <i class="bi bi-box-arrow-in-right me-2"></i>Login
+                    </button>
+                </form>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}
+
+{% block scripts %}
+<script>
+function togglePassword(inputId, btn) {
+    const input = document.getElementById(inputId);
+    const icon = btn.querySelector('i');
+    if (input.type === 'password') {
+        input.type = 'text';
+        icon.classList.replace('bi-eye', 'bi-eye-slash');
+    } else {
+        input.type = 'password';
+        icon.classList.replace('bi-eye-slash', 'bi-eye');
+    }
+}
+</script>
+{% endblock %}