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/en/baraql.md

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+# BaraQL - Query Language Reference
+
+BaraQL is a SQL-compatible query language with extensions for graph, vector, and document operations.
+
+## Basic Queries
+
+### 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 = 'Alice';
+```
+
+## Aggregates and Grouping
+
+```sql
+SELECT department, count(*), avg(salary)
+FROM employees
+GROUP BY department
+HAVING count(*) > 5;
+
+SELECT count(*), sum(amount), avg(price) FROM orders;
+```
+
+## 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;
+
+-- Multiple JOINs
+SELECT *
+FROM orders o
+JOIN users u ON o.user_id = u.id
+JOIN products p ON o.product_id = p.id;
+```
+
+## CTEs (Common Table Expressions)
+
+```sql
+-- Single CTE
+WITH active_users AS (
+  SELECT * FROM users WHERE active = true
+)
+SELECT * FROM active_users;
+
+-- Multiple CTEs
+WITH
+  recent AS (SELECT * FROM orders WHERE date > '2025-01-01'),
+  totals AS (SELECT user_id, sum(amount) as total FROM recent GROUP BY user_id)
+SELECT u.name, t.total FROM users u JOIN totals t ON u.id = t.user_id;
+```
+
+## Subqueries
+
+```sql
+-- Subquery in FROM
+SELECT * FROM (SELECT id, name FROM users WHERE active = true) AS active;
+
+-- EXISTS subquery
+SELECT name FROM users WHERE EXISTS (SELECT 1 FROM orders WHERE orders.user_id = users.id);
+```
+
+## CASE Expressions
+
+```sql
+SELECT name,
+  CASE
+    WHEN age < 18 THEN 'minor'
+    WHEN age < 65 THEN 'adult'
+    ELSE 'senior'
+  END AS category
+FROM users;
+```
+
+## Schema Definition
+
+```sql
+CREATE TYPE Person {
+  name: str,
+  age: int32
+};
+
+CREATE TYPE Movie {
+  title: str,
+  director: Person
+};
+```
+
+## Vector Search
+
+```sql
+-- Insert with vector
+INSERT articles {
+  title := 'Nim Programming',
+  embedding := [0.1, 0.2, 0.3, ...]
+};
+
+-- Similarity search
+SELECT title FROM articles
+ORDER BY cosine_distance(embedding, [0.1, 0.2, 0.3, ...])
+LIMIT 5;
+```
+
+## Graph Patterns
+
+```sql
+MATCH (p:Person)-[:KNOWS]->(friend:Person)
+WHERE p.name = 'Alice'
+RETURN friend.name;
+```
+
+## Full-Text Search
+
+```sql
+SELECT * FROM articles
+WHERE MATCH(title, body) AGAINST('database programming');
+```
+
+## Supported Keywords
+
+| Category | Keywords |
+|----------|----------|
+| DQL | SELECT, FROM, WHERE, ORDER BY, GROUP BY, HAVING, LIMIT, OFFSET |
+| DML | INSERT, UPDATE, DELETE, SET |
+| DDL | CREATE TYPE, DROP TYPE, CREATE INDEX |
+| Join | INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN, CROSS JOIN |
+| Set | UNION, INTERSECT, EXCEPT |
+| CTEs | WITH, AS |
+| Case | CASE, WHEN, THEN, ELSE, END |
+| Graph | MATCH, RETURN, WHERE |
+| FTS | MATCH, AGAINST |