Update Firebird configuration and documentation

docs/databases/firebird.mdx

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+# @sequelize/firebird
+
+> Firebird dialect for [Sequelize v7](https://sequelize.org/), backed by [node-firebird](https://github.com/hgourvest/node-firebird).
+
+---
+
+## Installation (inside the monorepo)
+
+1. Copy this folder to `packages/firebird` inside the Sequelize monorepo.
+2. Register the package in the root `lerna.json` (it is auto-discovered via `packages/*`).
+3. Add `node-firebird` as a dependency and run:
+
+```powershell
+yarn install
+yarn build
+```
+
+---
+
+## Usage
+
+```ts
+import { Sequelize } from '@sequelize/core';
+import { FirebirdDialect } from '@sequelize/firebird';
+
+const sequelize = new Sequelize({
+  dialect: FirebirdDialect,
+  host: 'localhost',
+  port: 3050,
+  database: 'C:/data/myapp.fdb', // full path on the server
+  username: 'SYSDBA',
+  password: 'masterkey',
+  dialectOptions: {
+    charset: 'UTF8',
+    blobAsText: true,
+  },
+  omitNull: true,
+});
+
+await sequelize.authenticate();
+```
+
+---
+
+## Firebird-specific Quirks Handled
+
+| Standard SQL       | Firebird equivalent                  | Notes                             |
+| ------------------ | ------------------------------------ | --------------------------------- |
+| `LIMIT n OFFSET m` | `FIRST n SKIP m`                     | Injected after `SELECT`           |
+| `AUTOINCREMENT`    | `SEQUENCE` + `BEFORE INSERT TRIGGER` | Created automatically on `sync()` |
+| `TRUNCATE TABLE`   | `DELETE FROM`                        | No sequence reset                 |
+| `RENAME TABLE`     | ❌ not supported                     | Throws error                      |
+| `JSON` column      | `BLOB SUB_TYPE TEXT`                 | No JSON operators                 |
+| `TINYINT`          | `SMALLINT`                           | No 8-bit int in Firebird          |
+| `UUID`             | `CHAR(36)`                           | No native UUID type               |
+| `BOOLEAN`          | `BOOLEAN`                            | Requires Firebird 3.0+            |
+| Identifiers        | Double-quoted `"name"`               | Case-sensitive when quoted        |
+| Scalar `SELECT`    | `FROM RDB$DATABASE`                  | Firebird's "dual" table           |
+
+---
+
+## Data Type Mapping
+
+| Sequelize                | Firebird SQL         | Notes                  |
+| ------------------------ | -------------------- | ---------------------- |
+| `DataTypes.STRING(n)`    | `VARCHAR(n)`         |                        |
+| `DataTypes.TEXT`         | `BLOB SUB_TYPE TEXT` |                        |
+| `DataTypes.CHAR(n)`      | `CHAR(n)`            |                        |
+| `DataTypes.INTEGER`      | `INTEGER`            |                        |
+| `DataTypes.BIGINT`       | `BIGINT`             |                        |
+| `DataTypes.SMALLINT`     | `SMALLINT`           |                        |
+| `DataTypes.TINYINT`      | `SMALLINT`           | No TINYINT in Firebird |
+| `DataTypes.FLOAT`        | `FLOAT`              |                        |
+| `DataTypes.DOUBLE`       | `DOUBLE PRECISION`   |                        |
+| `DataTypes.DECIMAL(p,s)` | `DECIMAL(p,s)`       |                        |
+| `DataTypes.BOOLEAN`      | `BOOLEAN`            | Firebird 3+            |
+| `DataTypes.DATE`         | `TIMESTAMP`          |                        |
+| `DataTypes.DATEONLY`     | `DATE`               |                        |
+| `DataTypes.TIME`         | `TIME`               |                        |
+| `DataTypes.UUID`         | `CHAR(36)`           |                        |
+| `DataTypes.BLOB`         | `BLOB`               |                        |
+| `DataTypes.JSON`         | `BLOB SUB_TYPE TEXT` | No JSON operators      |