refactor: compose shared Wecom client and add subpath exports

[witjs]

Summary

Architecture refactor for the WeCom SDK client layer:

Before

• Business modules (User, Message, Agent, …) inherited Wecom
• Sharing transport/token across modules relied on Wecom.setGlobal() or constructing many clients with duplicated config
• Package only exported the root barrel (no first-class subpath imports)

After

• WecomModule composition: modules take ClientSource = Partial<WecomConfig> | Wecom and share one Wecom instance
• RequestKernel: shared request/retry/error policy used by Wecom and unauthenticated clients like Webhook
• createClient / createScope: preferred factories for shared clients and multi-tenant scopes (no process-wide globals)
• Suite.corp / corpWecom / createCorpClient and Hardware.device / deviceWecom / createDeviceClient for typed corp/device helpers
• package.json exports: wecom/user, wecom/message, wecom/client, … plus matching tsdown entries

Compatibility

• new User(config) / new Message(config) still work
• Modules also accept an existing Wecom instance
• Message supports default agentId (override per send / payload)
• Wecom.setGlobal() remains but is deprecated in favor of createClient / createScope

Examples

import { createClient } from 'wecom';
// or: import { User } from 'wecom/user';

const client = createClient({
  corpId: process.env.CORPID!,
  corpSecret: process.env.TEST_SECRET!,
  agentId: Number(process.env.TEST_AGENT_ID),
});
await client.user.get('alice');
await client.message.send({ touser: 'alice', msgtype: 'text', text: { content: 'hi' } });

const corp = suite.corp({ authCorpId, permanentCode });
const message = new Message(corp);
// or: suite.createCorpClient({ authCorpId, permanentCode, agentId })

Test plan

• pnpm install && pnpm typecheck
• pnpm test (unit + contract + types; mock fetch)
• Spot-check createClient sharing (single token refresh across modules)
• Spot-check new User(config) / new Message(wecom) compatibility
• Spot-check subpath import import { User } from 'wecom/user' after pnpm build
• Docs pages for config / identities / suite still render

Notes

Pushed via GitHub MCP (create_branch + push_files / create_or_update_file) because shell had no usable GH_TOKEN for git push. Branch tip may include multiple incremental commits rather than the single local 4823fd7 commit; content targets the local refactor tree.

A few guide/API doc pages and large test files (identity / modules / endpoints) may still need a follow-up sync if CI shows drift vs local /workspace/wecom.