docs: revise consumed REST services proposal with full CREATE support

Expand scope from read-only SHOW/DESCRIBE to include CREATE/DROP.
Add complete BSON type hierarchy, MDL syntax specification aligned
with example file, BSON-to-MDL mapping tables, revised grammar rules,
and phased implementation plan.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako