docs: data/CONTRIBUTING.md's lat/lng range doc contradicts the global schema and dataset

[yakew7]

Problem

data/CONTRIBUTING.md (the single source of truth for the place-record schema, per its own opening line) still tells contributors:

- `lat`/`lng`: from Google Maps (right-click pin, "What's here?"). Range: lat 18-20, lng 72-73.

That's the Mumbai Metropolitan Region's bounding box. It directly contradicts:

1. The actual schema it claims to be documenting — data/places.schema.json allows the full global range:

   $ python3 -c "
   import json
   s = json.load(open('data/places.schema.json'))
   print(s['properties']['lat'])
   print(s['properties']['lng'])
   "
   {'type': 'number', 'minimum': -90, 'maximum': 90}
   {'type': 'number', 'minimum': -180, 'maximum': 180}
   

2. The actual dataset — sat_centre.json alone has 608 places across 371 cities on 5+ continents, none of which are anywhere near lat 18-20 / lng 72-73 (e.g. Istanbul, Dubai, Seoul, London, Nairobi, Ankara).
3. studymap.config.ts, already fixed by chore: studymap.config bounds/cities contradict the now-global dataset (two sources of truth) #156 to describe cities as "any city worldwide... not just Mumbai/Thane/Navi Mumbai."

A new contributor adding a place outside Mumbai who reads this line literally would think their valid coordinates are out of range, or wonder if the tool only wants Mumbai places — exactly the kind of contributor-facing friction the rest of this file (and #156) was written to remove.

Fix

Delete the stale "Range: lat 18-20, lng 72-73" sentence (or replace it with the real constraint, i.e. "any real-world coordinate, validated against -90..90 / -180..180 by places.schema.json").

Acceptance criteria

• data/CONTRIBUTING.md's lat/lng field description no longer references the Mumbai bounding box