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/fts.md

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+# Full-Text Search Engine
+
+Inverted index with BM25 and TF-IDF ranking for text search.
+
+## Usage
+
+```nim
+import barabadb/fts/engine
+
+var idx = newInvertedIndex()
+idx.addDocument(1, "Nim is a fast programming language")
+idx.addDocument(2, "Python is popular for data science")
+
+# BM25 search
+let results = idx.search("programming language")
+
+# TF-IDF search
+let tfidf = idx.searchTfidf("programming language")
+
+# Fuzzy search (typo tolerance)
+let fuzzy = idx.fuzzySearch("programing", maxDistance = 2)
+
+# Wildcard search
+let wild = idx.regexSearch("prog*")
+```
+
+## Ranking Methods
+
+### BM25
+
+Best matching ranking algorithm:
+
+```nim
+let bm25 = idx.searchBM25("query terms")
+```
+
+### TF-IDF
+
+Term Frequency-Inverse Document Frequency:
+
+```nim
+let tfidf = idx.searchTfidf("query terms")
+```
+
+## Search Features
+
+| Feature | Description |
+|---------|-------------|
+| Fuzzy search | Levenshtein distance tolerance |
+| Wildcard | Prefix, suffix, and infix wildcards |
+| Regex | Regular expression patterns |
+| Phrase search | Exact phrase matching |
+| Boolean | AND, OR, NOT operators |
+
+## Multi-Language Support
+
+```nim
+import barabadb/fts/multilang
+
+# Supported languages: EN, BG, DE, FR, RU
+var tokenizer = newTokenizer("bg")  # Bulgarian
+let tokens = tokenizer.tokenize("Търсене в пълен текст")
+```
+
+Features per language:
+- Tokenization
+- Stop words
+- Stemming
+- Language detection