fix: validate dial timeouts before ATD

[Justinabox]

Summary

• validate public CallService.dial() timeouts before call state changes, logging, or ATD writes
• reject zero, negative, boolean, non-finite, and non-numeric timeout values with a generic ValueError
• redact outbound dial commands in executor debug/error display without changing the actual command sent to the modem

Closes #288.

Verification

• git diff --check
• PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/test_call_service.py tests/test_executor.py -q → 130 passed
• PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/ -q → 1102 passed

Risks

• Narrow validation and log-display-only change. Real modem writes are covered by mock-transport tests; no hardware was contacted.

[Justinabox]

Release review: needs-fix before landing.

The dial-timeout validation is fail-closed before FSM mutation and modem I/O, but the new executor privacy rule only redacts ATD...;. Modem.execute() exposes raw AT commands, so ATD<destination> without the terminal semicolon (and whitespace-suffixed variants) still appears in executor DEBUG TX/RX/timeout logging.

Please make ATD command redaction fail closed across raw command forms, and add focused executor/raw-AT regressions covering non-semicolon and whitespace variants in TX, echoed RX, idle delayed echo, and timeout diagnostics. Preserve the current public timeout behavior. Re-run the full repository gate after the fresh RED/GREEN test cycle.