feat: migrate localStorage to backend storage with declarative persist plugin

- Add backendPersist Pinia plugin for declarative preferences.json persistence
- Move Preferences types to @openchatlab/shared-types (single source of truth)
- Migrate sessionGapThreshold from localStorage to config.toml [ui]
- Migrate chatlab_filter_history from localStorage to preferences.json
- Fix stale localStorage locale read in i18n/index.ts
- Simplify usePreferencesSync (172 → 75 lines) by delegating to plugin

Adding a new backend-synced preference now only requires 3 changes:
1. shared-types interface  2. node-runtime DEFAULTS  3. store backendPersist.pick

apps/cli/src/http/index.ts

@@ -25,6 +25,7 @@ import { registerSessionRoutes } from './routes/sessions'
 import { registerWebRoutes } from './routes/web'
 import { registerNlpRoutes } from './routes/nlp'
 import { registerAiRoutes } from './routes/ai'
+import { registerPreferencesRoutes } from './routes/preferences'
 import { initServerAiLogger, closeServerAiLogger } from '../ai/logger'
 import { initSync, cleanupSync } from '../sync'
 
@@ -133,6 +134,7 @@ export async function startHttpServer(options?: HttpServerOptions): Promise<{
   registerNlpRoutes(server, dbManager)
   registerAiRoutes(server, dbManager, convManager)
   registerWebRoutes(server, dbManager, { pathProvider, nativeBinding })
+  registerPreferencesRoutes(server, pathProvider)
 
   initSync(server, dbManager, pathProvider, { port, host, token })
 

apps/cli/src/http/routes/preferences.ts

@@ -0,0 +1,58 @@
+/**
+ * Preferences HTTP routes — /_web/preferences/*
+ *
+ * Read/write preferences.json and config.toml [ui] section for Web UI.
+ */
+
+import type { FastifyInstance } from 'fastify'
+import { PreferencesManager, type Preferences } from '@openchatlab/node-runtime'
+import { loadConfig, writeConfigField, type UiConfig } from '@openchatlab/config'
+import type { PathProvider } from '@openchatlab/core'
+
+let prefManager: PreferencesManager | null = null
+
+export function registerPreferencesRoutes(server: FastifyInstance, pathProvider: PathProvider): void {
+  if (!prefManager) {
+    prefManager = new PreferencesManager(pathProvider.getSystemDir())
+  }
+
+  server.get('/_web/preferences', async () => {
+    return prefManager!.load()
+  })
+
+  server.patch<{ Body: Partial<Preferences> }>('/_web/preferences', async (request) => {
+    return prefManager!.save(request.body)
+  })
+
+  server.get('/_web/preferences/ui-config', async () => {
+    const config = loadConfig()
+    return config.ui
+  })
+
+  server.patch<{ Body: Partial<UiConfig> }>('/_web/preferences/ui-config', async (request) => {
+    try {
+      for (const [key, value] of Object.entries(request.body)) {
+        if (value !== undefined) {
+          writeConfigField('ui', key, value as string | number)
+        }
+      }
+      return { success: true }
+    } catch (err) {
+      return { success: false, error: err instanceof Error ? err.message : String(err) }
+    }
+  })
+
+  server.get('/_web/preferences/locale', async () => {
+    const config = loadConfig()
+    return { lang: config.locale.lang }
+  })
+
+  server.patch<{ Body: { lang: string } }>('/_web/preferences/locale', async (request) => {
+    try {
+      writeConfigField('locale', 'lang', request.body.lang)
+      return { success: true }
+    } catch (err) {
+      return { success: false, error: err instanceof Error ? err.message : String(err) }
+    }
+  })
+}