fix(runtime): readable config error when TELEGRAM_API_ID/HASH are missing - #312

Before

Starting the server without TELEGRAM_API_ID dies with a raw traceback that never mentions what is actually missing:

$ uv run main.py
Traceback (most recent call last):
  File "main.py", line 14, in <module>
    from telegram_mcp import runtime as _runtime
  ...
  File "telegram_mcp/runtime.py", line 153, in <module>
    TELEGRAM_API_ID = int(os.getenv("TELEGRAM_API_ID"))
TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType'

A non-numeric value fails the same way:

TypeError: int() argument must be... — for TELEGRAM_API_ID="1a2b": ValueError: invalid literal for int() with base 10: '1a2b'

The sibling entrypoints (migrate_session.py, session_string_generator.py) already print a readable message; only the server crashes.

After

Same startup now exits with a config error that names the variables and what to do, in the same style as the siblings:

$ uv run main.py
Error: TELEGRAM_API_ID and TELEGRAM_API_HASH must be set. Create an .env file with your credentials from https://my.telegram.org/apps

A malformed value gets its own message instead of a ValueError:

Error: TELEGRAM_API_ID must be an integer

What changed

telegram_mcp/runtime.py: the module-level int(os.getenv("TELEGRAM_API_ID")) is replaced with _require_api_credentials(), which validates presence, non-emptiness, and integer format before use and exits with the messages above. No behavior change when credentials are set correctly.

Tests

• test_missing_api_credentials_exit_with_readable_error, test_non_integer_api_id_exits_with_readable_error in tests/test_runtime.py
• Full suite (uv run pytest): 1198 passed on the tree with this and the two sibling fixes (migrate_session turns '-' into '_' in account labels; generator and runtime keep the dash #301, save_aliases crashes when TELEGRAM_ALIASES_FILE points into a missing directory #302)

Fixes #300

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