fix(callback): add null guards and try-catch wrapper to callback query handler (issue #20)

[xdevrobot]

Summary

Fixes MEDIUM — Runtime Crash / Type Confusion in the callback query handler. Unsafe type assertions on Telegram update objects could cause TypeError crashes when GramJS returns an unexpected shape. Any unhandled error would kill the callback query handler for all future queries.

Root Cause

The handler at src/index.ts:1237 had five unsafe patterns:

1. queryId passed directly to answerCallbackQuery() without null-check
2. data?.toString() — if data exists but lacks toString(), it crashes
3. Number(undefined) → NaN for msgId (silent)
4. Number(undefined) → NaN for userId (silent)
5. No try-catch — any error kills the handler permanently

Changes

src/index.ts — callback query handler

• Early return on missing queryId: If queryId is null/undefined, skip processing (can't answer without it)
• Early return on missing data: If data is empty or not parseable, skip dispatch
• Safe toString() check: typeof callbackUpdate.data?.toString === "function" instead of assuming the method exists
• Number.isFinite guards: messageId and userId default to 0 instead of NaN
• Outer try-catch: Wraps the entire handler body — malformed updates are logged but never kill the handler

Robustness Improvements

Issue	Before	After
Missing queryId	Passed to GramJS (crash)	Early return
data without toString()	TypeError crash	typeof guard → empty string → early return
msgId: undefined	NaN	0 (via Number.isFinite)
userId: undefined	NaN	0 (via Number.isFinite)
Any unhandled error	Handler dies permanently	Caught, logged, handler survives

Closes #20

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