Add multi-database adapter support (MySQL, PostgreSQL, SQLite) + update README and screenshots

[Copilot]

Extends the library beyond SQLite to support MySQL/MariaDB and PostgreSQL via a pluggable adapter layer. Schema introspection is automatic (via information_schema / PRAGMA) — no manual table mapping required. All existing SQLite APIs are preserved unchanged.

Adapter architecture

• IDatabaseAdapter — common interface; defines quoteIdentifier() for dialect-aware quoting plus all CRUD/introspection operations
• SqliteAdapter — thin wrapper around the existing databaseFunctions module; zero behaviour change
• MysqlAdapter — mysql2/promise pool; reflects via information_schema.TABLES/COLUMNS/KEY_COLUMN_USAGE
• PostgresAdapter — pg Pool; reflects via information_schema.tables/columns/table_constraints
• mysql2 and pg added as optionalDependencies

New entry point

// MySQL / MariaDB
import mysql from "mysql2/promise";
import { MysqlAdapter, SqliteGuiNodeWithAdapter } from "sqlite-gui-node";
SqliteGuiNodeWithAdapter(new MysqlAdapter(mysql.createPool({ host, user, password, database })), 8080);

// PostgreSQL
import { Pool } from "pg";
import { PostgresAdapter, SqliteGuiNodeWithAdapter } from "sqlite-gui-node";
SqliteGuiNodeWithAdapter(new PostgresAdapter(new Pool({ host, user, database })), 8080);

Legacy SqliteGuiNode / SqliteGuiNodeMiddleware / createSqliteGuiApp are kept and internally wrap Database in SqliteAdapter.

SQL generator refactor

• generateInsertSQL now accepts IDatabaseAdapter instead of raw db: any
• generateUpdateSQL / generateCreateTableSQL accept an optional quoter function (default: identity — no quoting), which also fixes 2 pre-existing test failures caused by hardcoded backtick quoting in expected strings

README + screenshots

Updated to reflect the redesigned UI and multi-db support — new sections for MySQL/PostgreSQL usage, updated Arguments table, and 4 fresh screenshots of the current dark-sidebar layout.

Screenshots

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