fix(gateway): resolve two startup bugs blocking E2E testing

BUG-1: Extract PLUGIN_REGISTRY to plugin.tokens.ts to break ESM
circular reference between plugin.module.ts and plugin.service.ts.
Was causing ReferenceError at startup.

BUG-2: Replace AuthStorage.create() with AuthStorage.inMemory() in
ProviderService. The file-based auth storage resolves ~/.pi/auth.json
which causes silent process exit in server context.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/gateway/src/agent/provider.service.ts

@@ -9,7 +9,7 @@ export class ProviderService implements OnModuleInit {
   private registry!: ModelRegistry;
 
   async onModuleInit(): Promise<void> {
-    const authStorage = AuthStorage.create();
+    const authStorage = AuthStorage.inMemory();
     this.registry = new ModelRegistry(authStorage);
 
     this.registerOllamaProvider();

apps/gateway/src/plugin/plugin.module.ts

@@ -10,8 +10,7 @@ import { DiscordPlugin } from '@mosaic/discord-plugin';
 import { TelegramPlugin } from '@mosaic/telegram-plugin';
 import { PluginService } from './plugin.service.js';
 import type { IChannelPlugin } from './plugin.interface.js';
-
-export const PLUGIN_REGISTRY = Symbol('PLUGIN_REGISTRY');
+import { PLUGIN_REGISTRY } from './plugin.tokens.js';
 
 class DiscordChannelPluginAdapter implements IChannelPlugin {
   readonly name = 'discord';

apps/gateway/src/plugin/plugin.service.ts

@@ -1,5 +1,5 @@
 import { Inject, Injectable } from '@nestjs/common';
-import { PLUGIN_REGISTRY } from './plugin.module.js';
+import { PLUGIN_REGISTRY } from './plugin.tokens.js';
 import type { IChannelPlugin } from './plugin.interface.js';
 
 @Injectable()

apps/gateway/src/plugin/plugin.tokens.ts

@@ -0,0 +1 @@
+export const PLUGIN_REGISTRY = Symbol('PLUGIN_REGISTRY');