feat(translations): add Simplified Chinese (zh-Hans)

[MF-142]

add Simplified Chinese language

Summary

Added Simplified Chinese (zh-Hans) translation for the CAP Alerts integration to improve accessibility for Chinese-speaking users.

Changes

Added custom_components/cap_alerts/translations/zh-Hans.json

Test Plan

• pytest tests -q passes
• ruff check custom_components/ tests/ scripts/ passes
• ruff format --diff custom_components/ tests/ scripts/ is clean
• mypy custom_components/cap_alerts passes
• Loaded in a running Home Assistant instance (for behavior changes)
• Dependency order respected (model → providers → coordinator → sensor → config_flow → init)

[seevee]

Thanks for this, merging shortly.

Checked before merge:

• Key structure matches strings.json and translations/en.json exactly. No missing or extra keys in either direction.
• No untranslated leftovers (no values identical to the English source).
• UTF-8, LF, trailing newline, 2-space indent matching en.json.
• Hassfest, Lint, Test, Type check all green.

I spot-checked the strings that carry real information and they're accurate: the September 2026 legacy-host retirement in feed_source, the "fails loud if the country does not publish geometry" warning on the GPS-polygon steps, and the NEW/CON/CAN entity-recreation caveat on wmo_source.

Some non-blocking notes for a later PR if you want them:

• "feed" is translated two ways: 警报源 in the feed_source label, 馈送 in its own description and in streaming. Both show up in the same form.
• 追踪器 vs 跟踪器 for "tracker". HA core's zh-Hans uses 设备跟踪器 for device_tracker. Your call.
• zone_id is Zone ID(s) in English and the plural hint is dropped, though the description does say comma-separated.

Housekeeping:

• I'm squash-merging, so the intermediate commits collapse into one. eccc.py on your head commit is byte-identical to main, so the delete/recreate in the history isn't reverting anything.
• I'll extend tests/test_translation_keys_in_sync.py to cover all of translations/*.json in a follow-up. It only guards en.json right now, so this file could drift as new config-flow steps land.

再次感谢你的贡献！