fix: show database-specific options in Create Database dialog

[datlechin]

Summary

• Create Database dialog now shows correct options per database type instead of hardcoded MySQL charsets for all databases
• MySQL/MariaDB: Character Set + Collation (expanded from 4 to 14 charsets)
• PostgreSQL/Redshift: Encoding + LC_COLLATE (UTF8, LATIN1, SQL_ASCII, etc.)
• MongoDB/ClickHouse/MSSQL/BigQuery/CloudflareD1/DuckDB: Name only (no charset options)
• Redis/etcd: Create button hidden (databases are pre-allocated or unsupported)

Fixes "Invalid encoding: utf8mb4" error on PostgreSQL and "invalid LC_COLLATE locale name: utf8_unicode_ci" error.

Changes

• New CreateDatabaseOptions model with per-database-type config (follows CreateTableOptions pattern)
• Refactored CreateDatabaseSheet to accept databaseType and render form conditionally
• Expanded MySQL plugin charset whitelist (4 -> 14)
• Expanded PostgreSQL/Redshift plugin encoding whitelist (3 -> 11)
• Hidden create button for Redis and etcd

Test plan

• MySQL: Create Database shows Character Set + Collation with 14 charsets
• PostgreSQL: Create Database shows Encoding + LC_COLLATE with UTF8 default
• MongoDB/MSSQL/ClickHouse: Create Database shows name field only
• Redis: Create button not visible in database switcher
• Create database succeeds on MySQL and PostgreSQL without errors

[datlechin]

Superseded by #690 which includes all Create Database fixes plus the sidebar architecture refactor.