docs(plugins): add Fiber plugin page (EN + RU)

Assisted-By: Claude Fable 5 (1M context) <noreply@anthropic.com>

Author: roxblnfk

.vitepress/config.mts

@@ -107,6 +107,7 @@ gtag('config', 'G-VYGDN3X0PR');`],
                 { text: 'Data Providers', link: '/docs/plugins/data.md' },
                 { text: 'Retry', link: '/docs/plugins/retry.md' },
                 { text: 'Repeat', link: '/docs/plugins/repeat.md' },
+                { text: 'Fiber', link: '/docs/plugins/fiber.md' },
                 { text: 'Bench', link: '/docs/plugins/bench.md' },
                 { text: '\#[Test]', link: '/docs/plugins/test.md' },
                 { text: 'Lifecycle', link: '/docs/plugins/lifecycle.md' },