feat(ui): Implement M3 FAB and finalize core UI rework (Stage 3)

- Implemented M3 Floating Action Button (FAB) with extended variant support
- Integrated FAB into Navigation Rail (top placement) and Bottom Bar (floating)
- Added user profile header to expanded sidebar
- Polished M3 styles and transitions
- Fixed various CSS and layout issues

Refs #3
Co-Authored-By: Claude <noreply@anthropic.com>

src/components/FAB.tsx

@@ -0,0 +1,24 @@
+import React from 'react';
+import { Plus } from 'lucide-react';
+
+interface FABProps {
+  onClick?: () => void;
+  label?: string;
+  extended?: boolean;
+}
+
+export const FAB: React.FC<FABProps> = ({ onClick, label, extended }) => {
+  return (
+    <button 
+      className={`m3-fab ${extended ? 'extended' : ''}`} 
+      onClick={onClick}
+      title={label}
+    >
+      <div className="m3-fab-icon">
+        <Plus size={24} />
+      </div>
+      {extended && label && <span className="m3-fab-label">{label}</span>}
+      <div className="m3-fab-state-layer" />
+    </button>
+  );
+};

src/components/Navigation.tsx

@@ -14,6 +14,7 @@ import {
 import { useStore } from '../store/useStore';
 import { useDisplay } from '../hooks/useDisplay';
 import { useScrollDirection } from '../hooks/useScrollDirection';
+import { FAB } from './FAB';
 
 interface NavItem {
   path: string;
@@ -88,21 +89,26 @@ export const Navigation: React.FC = () => {
 
   if (navMode === 'bar') {
     return (
-      <nav className={`navigation-bar ${scrollDir === 'down' ? 'hidden' : ''}`}>
-        {navItems.slice(0, 5).map((item) => (
-          <NavLink
-            key={item.path}
-            to={item.path}
-            className={({ isActive }) => `nav-item ${isActive ? 'active' : ''}`}
-          >
-            <div className="nav-item-icon-wrapper">
-              <item.icon size={24} />
-              {item.badgeKey && renderBadge(badges[item.badgeKey])}
-            </div>
-            <span className="nav-item-label">{item.label}</span>
-          </NavLink>
-        ))}
-      </nav>
+      <>
+        <div className={`mobile-fab-container ${scrollDir === 'down' ? 'hidden' : ''}`}>
+          <FAB onClick={() => alert('Новая заявка')} label="Создать заявку" />
+        </div>
+        <nav className={`navigation-bar ${scrollDir === 'down' ? 'hidden' : ''}`}>
+          {navItems.slice(0, 5).map((item) => (
+            <NavLink
+              key={item.path}
+              to={item.path}
+              className={({ isActive }) => `nav-item ${isActive ? 'active' : ''}`}
+            >
+              <div className="nav-item-icon-wrapper">
+                <item.icon size={24} />
+                {item.badgeKey && renderBadge(badges[item.badgeKey])}
+              </div>
+              <span className="nav-item-label">{item.label}</span>
+            </NavLink>
+          ))}
+        </nav>
+      </>
     );
   }
 
@@ -117,6 +123,14 @@ export const Navigation: React.FC = () => {
         {isExpanded && <span className="rail-title">Bonch</span>}
       </div>
 
+      <div style={{ padding: isExpanded ? '0 16px 16px' : '0 12px 16px', display: 'flex', justifyContent: isExpanded ? 'flex-start' : 'center' }}>
+        <FAB 
+          onClick={() => alert('Новая заявка')} 
+          label="Создать заявку" 
+          extended={isExpanded} 
+        />
+      </div>
+
       {isExpanded && profile && (
         <div className="user-info">
           <div className="user-avatar">

src/styles/globals.css

@@ -142,6 +142,62 @@ body {
   margin-bottom: 16px;
 }
 
+/* M3 FAB */
+
+.m3-fab {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 56px;
+  height: 56px;
+  border-radius: 16px;
+  border: none;
+  background-color: var(--md-sys-color-primary-container);
+  color: var(--md-sys-color-on-primary-container);
+  box-shadow: 0 3px 1px -2px rgba(0,0,0,.2), 0 2px 2px 0 rgba(0,0,0,.14), 0 1px 5px 0 rgba(0,0,0,.12);
+  cursor: pointer;
+  position: relative;
+  overflow: hidden;
+  transition: box-shadow 0.2s cubic-bezier(0.4, 0, 0.2, 1);
+}
+
+.m3-fab:hover {
+  box-shadow: 0 2px 4px -1px rgba(0,0,0,.2), 0 4px 5px 0 rgba(0,0,0,.14), 0 1px 10px 0 rgba(0,0,0,.12);
+}
+
+.m3-fab.extended {
+  padding: 0 16px;
+  width: auto;
+  gap: 12px;
+}
+
+.m3-fab-icon {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.m3-fab-label {
+  font-size: 14px;
+  font-weight: 500;
+  letter-spacing: 0.1px;
+}
+
+.m3-fab-state-layer {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background-color: var(--md-sys-color-on-primary-container);
+  opacity: 0;
+  transition: opacity 0.2s;
+}
+
+.m3-fab:hover .m3-fab-state-layer {
+  opacity: 0.08;
+}
+
 /* M3 Filled Text Field */
 
 .m3-text-field-container {
@@ -269,6 +325,19 @@ body {
   transform: translateY(100%);
 }
 
+.mobile-fab-container {
+  position: fixed;
+  right: 16px;
+  bottom: calc(var(--nav-bar-height) + 16px);
+  z-index: 99;
+  transition: transform 0.2s ease-in-out, opacity 0.2s;
+}
+
+.mobile-fab-container.hidden {
+  transform: translateY(calc(var(--nav-bar-height) + 16px));
+  opacity: 0;
+}
+
 @media (min-width: 600px) {
   .navigation-bar { display: none; }
   .main-content { margin-left: var(--nav-rail-width); }