Add unit tests for telegram-client.js and mcp-server.js

[dapi]

Problem

Project has vitest run configured but zero test files. CLAUDE.md recommends adding coverage when extending telegram-client.js or message-sync-service.js by mocking MTProto responses.

Proposed solution

Add unit tests starting with the most critical modules:

1. telegram-client.test.js — mock gramjs client.sendText/client.sendFile, verify:

   • sendTextMessage passes correct params (noWebpage, replyTo, parse mode)
   • sendFileMessage passes correct params
   • Input validation (empty text, missing file)
   • normalizeChannelId handling

2. mcp-server.test.js — test MCP tool handlers with mocked telegramClient:

   • Schema validation (zod schemas reject invalid input)
   • Handlers pass correct options to client methods
   • Response format

3. cli.test.js — test CLI option parsing:

   • --no-preview maps to noPreview: true
   • --parse-mode normalization
   • --topic / --reply-to parsing

Notes

• Use vitest
• Mock MTProto layer (gramjs) — no real Telegram calls
• Name files <module>.test.js in project root or tests/ directory
• Consider dependency injection or module mocking for TelegramClient

See also: #10 (added --no-preview without tests)