Integrate Bootstrap 5 and Bootstrap Icons into UI

- Add Bootstrap 5.3.3 + Icons via CDN to base.html
- Replace 315-line hand-written CSS with 35-line brand overrides
- Update all 13 templates with Bootstrap utility classes:
  - Responsive navbar with mobile hamburger menu
  - Consistent card-based layout for forms and profile
  - Proper button alignment with d-flex and d-grid utilities
  - List groups for data display (profile info)
  - Professional alerts and icons
- No backend changes, no build toolchain needed
- Responsive design works on mobile/tablet/desktop

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

web/templates/profile_delete.html

@@ -0,0 +1,41 @@
+{% extends "base.html" %}
+{% block title %}Удалить аккаунт — EvoSync{% endblock %}
+
+{% block content %}
+<div class="row justify-content-center">
+    <div class="col-sm-10 col-md-6 col-lg-5">
+        <div class="card shadow-sm mt-4 border-danger">
+            <div class="card-header bg-danger text-white">
+                <h1 class="h5 mb-0"><i class="bi bi-trash me-2"></i>Удалить аккаунт</h1>
+            </div>
+            <div class="card-body p-4">
+                <div class="alert alert-warning">
+                    <i class="bi bi-exclamation-triangle me-1"></i>
+                    <strong>Внимание!</strong> Это действие необратимо. Все ваши данные будут удалены.
+                </div>
+
+                {% if errors %}
+                <div class="alert alert-danger">
+                    {% for error in errors %}
+                    <div>{{ error }}</div>
+                    {% endfor %}
+                </div>
+                {% endif %}
+
+                <form method="post" action="/profile/delete">
+                    <div class="mb-4">
+                        <label for="password" class="form-label">Введите пароль для подтверждения</label>
+                        <input type="password" id="password" name="password" class="form-control" required>
+                    </div>
+                    <div class="d-flex gap-2">
+                        <button type="submit" class="btn btn-danger">
+                            <i class="bi bi-trash me-1"></i>Удалить мой аккаунт
+                        </button>
+                        <a href="/profile" class="btn btn-outline-secondary">Отмена</a>
+                    </div>
+                </form>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}