feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/packages/admin/src/components/ui/Layout/PageLayout.tsx

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @jsxRuntime automatic */
+/** @jsxImportSource hono/jsx */
+
+import {cn} from '@fluxer/admin/src/utils/ClassNames';
+import type {PropsWithChildren} from 'hono/jsx';
+
+export type PageLayoutMaxWidth = 'sm' | 'md' | 'lg' | 'xl' | '2xl' | '3xl' | '4xl' | '5xl' | '6xl' | '7xl';
+
+export interface PageLayoutProps {
+	maxWidth?: PageLayoutMaxWidth;
+	padding?: boolean;
+}
+
+const maxWidthClasses: Record<PageLayoutMaxWidth, string> = {
+	sm: 'max-w-sm',
+	md: 'max-w-md',
+	lg: 'max-w-lg',
+	xl: 'max-w-xl',
+	'2xl': 'max-w-2xl',
+	'3xl': 'max-w-3xl',
+	'4xl': 'max-w-4xl',
+	'5xl': 'max-w-5xl',
+	'6xl': 'max-w-6xl',
+	'7xl': 'max-w-7xl',
+};
+
+export function PageLayout({maxWidth = '7xl', padding = false, children}: PropsWithChildren<PageLayoutProps>) {
+	const classes = cn('mx-auto w-full', maxWidthClasses[maxWidth], padding && 'px-4 sm:px-6 lg:px-8');
+
+	return <div class={classes}>{children}</div>;
+}