data: add SAT centres for Japan (currently zero)

[yakew7]

Context

data/places/sat_centre.json currently has 608 records across 371 cities, spanning the US, UK, Nigeria, Turkey, UAE, South Korea, India, Canada, Germany, France, Spain, Kenya, South Africa, Singapore and Australia (most added via the country batches in #74-#83 and #225).

Japan has zero entries:

$ python3 -c "
import json
d = json.load(open('data/places/sat_centre.json'))
cities = set(p['city'] for p in d)
for c in ['tokyo','osaka','yokohama','nagoya','kyoto']:
    print(c, c in cities)
"
tokyo False
osaka False
yokohama False
nagoya False
kyoto False

The SAT is administered at real international-school test centres in Japan (Tokyo, Osaka, Yokohama, etc. all have College Board CEEB codes).

Task

Add verified SAT test centres for Japan to data/places/sat_centre.json, following the format and quality gate in data/CONTRIBUTING.md:

• id: <city-prefix>-sat-<number>, e.g. tokyo-sat-01
• type: "sat_centre", exam: "SAT", valid_till set to the next SAT administration
• Real coordinates from Google Maps, a working gmaps_link
• A source/citation and a 4.0+ / 50+ review Google Maps listing, per the quality gate

Acceptance criteria

• At least 5 real SAT centres added for Japan (Tokyo, Osaka, or other cities)
• npm run validate:places passes with no new errors
• Each record cites a source in the PR description