Fix gaps in live weather route forecasts

[TowerAlphaTheta15]

What changed and why

Live route weather could silently omit cities whose observations were still loading or unavailable. The remaining observations sounded like a complete outlook, while those omitted stretches could use simulated fallback weather and produce unreported rain or heavy rain. V could also announce a simulated forecast while the selected live source was merely loading.

This change accounts for each upcoming city in order, identifies loading and unavailable observations, distinguishes live weather changes from simulated fallback changes, and suppresses invented V forecasts while live data is pending.

What players or maintainers will notice

W route weather reports now name cities whose live observations are still loading or unavailable and warn when simulated fallback may apply. On the road, weather-change announcements identify whether the condition is a live observation near a named city or simulated fallback weather. V says live weather is still loading instead of speaking an Ahead forecast before the first observation arrives. These behaviors also apply when Live weather controls calendar is off.

Tests and checks run

• uv run pytest tests/test_weather_trip.py tests/test_real_weather.py tests/test_season.py tests/test_trip_resume.py tests/test_driving_cruise_weather.py tests/test_announcements.py -q
• uv run pytest tests/test_driving_features.py::test_live_route_weather_accounts_for_loading_and_unavailable_cities -q
• uv run ruff check src tests tools
• uv run python -m compileall src tests tools
• git diff --cached --check

Accessibility impact

All changes are spoken-text improvements on existing keyboard-accessible W and V paths. Regression tests capture the exact screen-reader output for partial live route data, live-weather loading, and simulated fallback identification.

Changelog

• I added a player-facing bullet under ## Unreleased in CHANGELOG.md, written in plain player language and matching the existing style.
• This change is not player-facing, and every commit message in this PR includes [skip changelog].