feat: design system overhaul — sidebar, AI chats, settings, brainstorm, color cleanup

- Sidebar: dynamic brand-accent colors, brainstorm section restyled
- AI chat general: popup panel with expand/collapse, hides when contextual AI open
- AI chat contextual: tabs reordered (Actions first), X close button, height fix
- Settings: all tabs restyled, 6 new color presets (sage, terracotta, iron, etc.)
- Global color cleanup: emerald/orange hardcoded → brand-accent dynamic
- Brainstorm page: orange → brand-accent throughout
- PageEntry animation component added to key pages
- Floating AI button: bg-brand-accent instead of hardcoded black
- i18n: all 15 locales updated with new AI/billing keys
- Billing: freemium quota tracking, BYOK, stripe subscription scaffolding
- Admin: integrated into new design
- AGENTS.md + CLAUDE.md project rules added

memento-note/lib/byok/validate-key.ts

@@ -0,0 +1,106 @@
+import type { AiGatewayProvider } from '@/lib/ai/router';
+
+const OPENAI_COMPAT = new Set<string>([
+  'openai',
+  'deepseek',
+  'openrouter',
+  'mistral',
+  'zai',
+  'minimax',
+  'glm',
+  'custom',
+  'lmstudio',
+]);
+
+async function validateOpenAiCompatible(
+  apiKey: string,
+  baseUrl: string,
+): Promise<void> {
+  const res = await fetch(`${baseUrl.replace(/\/$/, '')}/models`, {
+    headers: { Authorization: `Bearer ${apiKey}` },
+    signal: AbortSignal.timeout(10_000),
+  });
+  if (!res.ok) {
+    throw new Error(`Provider rejected the API key (${res.status})`);
+  }
+}
+
+async function validateAnthropic(apiKey: string): Promise<void> {
+  const res = await fetch('https://api.anthropic.com/v1/messages', {
+    method: 'POST',
+    headers: {
+      'x-api-key': apiKey,
+      'anthropic-version': '2023-06-01',
+      'content-type': 'application/json',
+    },
+    body: JSON.stringify({
+      model: 'claude-3-5-haiku-20241022',
+      max_tokens: 1,
+      messages: [{ role: 'user', content: 'ping' }],
+    }),
+    signal: AbortSignal.timeout(15_000),
+  });
+  if (res.status === 401 || res.status === 403) {
+    throw new Error('Provider rejected the API key');
+  }
+  if (res.status >= 500) {
+    throw new Error('Provider temporarily unavailable; try again');
+  }
+}
+
+async function validateGoogle(apiKey: string): Promise<void> {
+  const res = await fetch(
+    `https://generativelanguage.googleapis.com/v1beta/models?key=${encodeURIComponent(apiKey)}`,
+    { signal: AbortSignal.timeout(10_000) },
+  );
+  if (!res.ok) {
+    throw new Error(`Provider rejected the API key (${res.status})`);
+  }
+}
+
+const BASE_URLS: Partial<Record<AiGatewayProvider, string>> = {
+  deepseek: 'https://api.deepseek.com/v1',
+  openrouter: 'https://openrouter.ai/api/v1',
+  mistral: 'https://api.mistral.ai/v1',
+  zai: 'https://api.zukijourney.com/v1',
+  minimax: 'https://api.minimax.io/v1',
+  glm: 'https://open.bigmodel.ai/api/paas/v4',
+  openai: 'https://api.openai.com/v1',
+};
+
+export async function validateProviderApiKey(
+  provider: AiGatewayProvider,
+  apiKey: string,
+  baseUrl?: string,
+): Promise<void> {
+  if (!apiKey.trim()) {
+    throw new Error('API key is required');
+  }
+
+  if (provider === 'anthropic' || provider === 'anthropic_custom') {
+    await validateAnthropic(apiKey);
+    return;
+  }
+
+  if (provider === 'google') {
+    await validateGoogle(apiKey);
+    return;
+  }
+
+  if (provider === 'ollama' || provider === 'lmstudio') {
+    throw new Error('Local providers are not supported for BYOK');
+  }
+
+  if (OPENAI_COMPAT.has(provider)) {
+    const url = provider === 'custom'
+      ? baseUrl
+      : BASE_URLS[provider as AiGatewayProvider];
+    if (!url) {
+      throw new Error('Base URL is required for this provider');
+    }
+    await validateOpenAiCompatible(apiKey, url);
+    return;
+  }
+
+  throw new Error(`Unsupported provider: ${provider}`);
+}