Add comprehensive documentation with i18n support (EN/BG)

- Add docs/ folder with English (en/) and Bulgarian (bg/) documentation
- Create index.md with language switching and links
- English docs: installation, quickstart, architecture, baraql, storage,
  schema, lsm, btree, vector, graph, fts, columnar, transactions,
  distributed, protocol, udf, api-binary, api-http, api-websocket
- Bulgarian docs: installation, quickstart, architecture, baraql,
  schema, lsm, btree, vector, graph, fts, transactions, distributed
- Update README license to BSD 3-Clause
- Add LICENSE file with BSD 3-Clause text

docs/bg/baraql.md

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+# BaraQL - Референция на Езика
+
+BaraQL е SQL-съвместим език за заявки с разширения за графи, вектори и документи.
+
+## Основни Заявки
+
+### SELECT
+
+```sql
+SELECT name, age FROM users WHERE age > 18 ORDER BY name LIMIT 10;
+```
+
+### INSERT
+
+```sql
+INSERT users { name := 'Alice', age := 30 };
+```
+
+### UPDATE
+
+```sql
+UPDATE users SET age = 31 WHERE name = 'Alice';
+```
+
+### DELETE
+
+```sql
+DELETE FROM users WHERE name = 'Bob';
+```
+
+## Агрегати и Групиране
+
+```sql
+SELECT department, count(*), avg(salary)
+FROM employees
+GROUP BY department
+HAVING count(*) > 5;
+```
+
+## JOINs
+
+```sql
+-- INNER JOIN
+SELECT u.name, o.total
+FROM users u
+INNER JOIN orders o ON u.id = o.user_id;
+
+-- LEFT JOIN
+SELECT u.name, o.total
+FROM users u
+LEFT JOIN orders o ON u.id = o.user_id;
+```
+
+## CTEs (Common Table Expressions)
+
+```sql
+WITH active_users AS (
+  SELECT * FROM users WHERE active = true
+)
+SELECT * FROM active_users;
+```
+
+## CASE Изрази
+
+```sql
+SELECT name,
+  CASE
+    WHEN age < 18 THEN 'minor'
+    WHEN age < 65 THEN 'adult'
+    ELSE 'senior'
+  END AS category
+FROM users;
+```
+
+## Схема
+
+```sql
+CREATE TYPE Person {
+  name: str,
+  age: int32
+};
+```
+
+## Векторно Търсене
+
+```sql
+INSERT articles {
+  title := 'Nim Programming',
+  embedding := [0.1, 0.2, 0.3, ...]
+};
+
+SELECT title FROM articles
+ORDER BY cosine_distance(embedding, [0.1, 0.2, 0.3, ...])
+LIMIT 5;
+```
+
+## Графични Шаблони
+
+```sql
+MATCH (p:Person)-[:KNOWS]->(friend:Person)
+WHERE p.name = 'Alice'
+RETURN friend.name;
+```
+
+## Пълнотекстово Търсене
+
+```sql
+SELECT * FROM articles
+WHERE MATCH(title, body) AGAINST('database programming');
+```