feat(generate): improve OpenAPI example value generation

Add enum support (string, integer, number, boolean), integer/number
min/max/exclusive bounds, field-name heuristics for common string
fields (name, phone, address, etc.), additional string formats
(password, byte, ipv4, ipv6, hostname), array minItems support with
cap at 5, and minLength/maxLength string constraint enforcement.

Uses Unicode code point counting for length constraints to prevent
panics on non-ASCII field names.

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

Author: strefethen