docs(readme): overhaul for current API surface

Refresh every code example and add coverage for APIs introduced since the
last pass. Rename Plan to Statement, Blueprint to Table, GroupedQueries
to ParsedQuery. Fix set()/onConflict()/fromSelect() signatures. Document
whereRaw/whereColumn, Sequences, JSON setJsonPath, PG mode(), ClickHouse
quantiles and typed ASOF JOIN with AsofOperator, SERIAL types, CHECK
constraints, generated columns, composite PKs, userType(), ClickHouse
Engine enum + TTL, MariaDB RETURNING, partitionByHash count, and the
MongoDB field-update operators. Refresh the feature matrix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: abnegate