feat: add browser environment support with access token authentication

Enable the web client to run in plain browser environments alongside Telegram Mini App support:

- Server: Add CLI_API_TOKEN authentication path as alternative to Telegram initData
- Client: Add useAuthSource hook to detect and manage Telegram vs browser auth sources
- Client: Add usePlatform hook for platform abstraction with graceful haptic feedback degradation
- Client: Add LoginPrompt component for browser access token login
- Client: Extend useTheme to fall back to system prefers-color-scheme in browser
- Client: Migrate all direct HapticFeedback calls to use usePlatform hook

web/src/hooks/usePlatform.ts

@@ -0,0 +1,55 @@
+import { useMemo } from 'react'
+import { getTelegramWebApp } from './useTelegram'
+
+export type HapticStyle = 'light' | 'medium' | 'heavy' | 'rigid' | 'soft'
+export type HapticNotification = 'error' | 'success' | 'warning'
+
+export type PlatformHaptic = {
+    /** Trigger impact feedback */
+    impact: (style: HapticStyle) => void
+    /** Trigger notification feedback */
+    notification: (type: HapticNotification) => void
+    /** Trigger selection changed feedback */
+    selection: () => void
+}
+
+export type Platform = {
+    /** Whether running in Telegram Mini App */
+    isTelegram: boolean
+    /** Haptic feedback (no-op on browser) */
+    haptic: PlatformHaptic
+}
+
+function createHaptic(): PlatformHaptic {
+    return {
+        impact: (style: HapticStyle) => {
+            getTelegramWebApp()?.HapticFeedback?.impactOccurred(style)
+        },
+        notification: (type: HapticNotification) => {
+            getTelegramWebApp()?.HapticFeedback?.notificationOccurred(type)
+        },
+        selection: () => {
+            getTelegramWebApp()?.HapticFeedback?.selectionChanged()
+        }
+    }
+}
+
+// Singleton haptic instance (functions are stable)
+const haptic = createHaptic()
+
+export function usePlatform(): Platform {
+    const isTelegram = useMemo(() => getTelegramWebApp() !== null, [])
+
+    return {
+        isTelegram,
+        haptic
+    }
+}
+
+// Non-hook version for use outside React components
+export function getPlatform(): Platform {
+    return {
+        isTelegram: getTelegramWebApp() !== null,
+        haptic
+    }
+}