docs: add German (DE) documentation + update all docs for Sessions 10-12

New German documentation (docs/de/):
- index.md, quickstart.md, installation.md
- baraql.md, graph.md, vector.md, mcp.md

Updated English documentation:
- changelog.md: all Sessions 10-12 features
- graph.md: SQL GRAPH_TABLE, CREATE GRAPH, all 8 algorithms, Cypher, similarity_nodes, node2vec
- vector.md: hybrid RAG, chunk(), embed_text(), auto-embed, nl_to_sql(), schema_prompt()
- baraql.md: new AI & Cross-Modal Functions section, updated keyword tables
- mcp.md: MCP Server documentation (new file)
- index.md: added German (DE) language link

docs/de/quickstart.md

@@ -0,0 +1,134 @@
+# BaraDB — Schnellstart
+
+## Server starten
+
+```bash
+./build/baradadb
+```
+
+Der Server startet standardmäßig auf `localhost:9470`.
+
+## Verbindung via CLI
+
+```bash
+./build/baradadb --shell
+```
+
+## MCP Server (AI Agenten)
+
+```bash
+./build/baramcp --data-dir ./data
+```
+
+Der MCP Server startet im STDIO-Modus und stellt 3 Tools für AI-Agenten bereit: `query`, `vector_search`, `schema_inspect`.
+
+## Grundlegende Operationen
+
+### Tabelle erstellen
+
+```sql
+CREATE TABLE users (
+    id INTEGER PRIMARY KEY,
+    name TEXT,
+    email TEXT,
+    age INTEGER
+);
+```
+
+### Daten einfügen
+
+```sql
+INSERT INTO users (id, name, email, age) VALUES (1, 'Alice', 'alice@test.com', 30);
+INSERT INTO users (id, name, email, age) VALUES (2, 'Bob', 'bob@test.com', 25);
+```
+
+### Daten abfragen
+
+```sql
+SELECT name, age FROM users WHERE age > 18;
+```
+
+### Indizes erstellen
+
+```sql
+-- BTree Index
+CREATE INDEX idx_name ON users(name) USING btree;
+
+-- Volltext-Index
+CREATE INDEX idx_email_fts ON users(email) USING fts;
+
+-- Vektor-Index
+CREATE INDEX idx_vec ON items(embedding) USING hnsw;
+```
+
+## Vector Search
+
+```sql
+CREATE TABLE docs (id INTEGER PRIMARY KEY, content TEXT, embedding VECTOR(768));
+CREATE INDEX docs_vec ON docs(embedding) USING hnsw;
+
+-- Ähnlichkeitssuche
+SELECT id, cosine_distance(embedding, '[0.1, 0.2, ...]') AS dist
+FROM docs ORDER BY dist ASC LIMIT 10;
+```
+
+## Graph Engine
+
+```sql
+CREATE GRAPH social;
+INSERT INTO social_nodes (id, node_label) VALUES (1, 'Alice'), (2, 'Bob');
+INSERT INTO social_edges (source_id, dest_id) VALUES (1, 2);
+
+-- BFS Traversal
+SELECT * FROM GRAPH_TABLE(social MATCH (n)-[r]->(m) ALGORITHM bfs COLUMNS (id, node_label));
+
+-- PageRank
+SELECT * FROM GRAPH_TABLE(social ALGORITHM pagerank COLUMNS (id, node_label, rank));
+
+-- Community Detection (Louvain)
+SELECT * FROM GRAPH_TABLE(social ALGORITHM community COLUMNS (id, node_label, community));
+
+-- Kürzester Pfad
+SELECT * FROM GRAPH_TABLE(social ALGORITHM shortest_path START 1 END 2 COLUMNS (id, node_label));
+
+-- Knoten-Ähnlichkeit (Jaccard)
+SELECT similarity_nodes('social', 'jaccard') AS result;
+```
+
+## AI Pipeline
+
+```sql
+-- Text in Chunks zerlegen
+SELECT chunk('Langer Text hier...', 1024, 128) AS result;
+
+-- Embedding generieren (mit konfiguriertem externen Service)
+SELECT embed_text('Suchanfrage') AS result;
+
+-- Schema-Prompt für LLM generieren
+SELECT schema_prompt('users') AS result;
+
+-- Natural Language → SQL (mit konfiguriertem LLM)
+SELECT nl_to_sql('Zeige alle Benutzer über 25', 'users') AS result;
+
+-- Cypher zu BaraQL übersetzen
+SELECT cypher('MATCH (a)-[r]->(b) RETURN a.node_label, b.node_label') AS result;
+```
+
+## HTTP/REST API
+
+```bash
+curl -X POST http://localhost:9470/query \
+  -H "Content-Type: application/json" \
+  -d '{"query": "SELECT * FROM users"}'
+```
+
+## Konfiguration
+
+```bash
+# Umgebungsvariablen
+export BARADB_DATA_DIR=./data
+export BARADB_EMBED_ENDPOINT=http://localhost:11434/api/embeddings
+export BARADB_EMBED_MODEL=nomic-embed-text
+export BARADB_LLM_ENDPOINT=http://localhost:11434/api/generate
+export BARADB_LLM_MODEL=llama3
+```