docs: synchronize documentation across all languages

- Add mcp.md to: bg, fa, ru, tr, zh, ar
- Add index.md to Bulgarian (bg)
- Add 24 missing German (de) documentation files

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docs/de/columnar.md

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+# Kolumnare Speicherung
+
+Spaltenorientierte Speicherung für analytische Abfragen und Aggregation.
+
+## Verwendung
+
+```nim
+import barabadb/core/columnar
+
+var batch = newColumnBatch()
+var ageCol = batch.addInt64Col("age")
+var nameCol = batch.addStringCol("name")
+
+ageCol.appendInt64(25)
+nameCol.appendString("Alice")
+```
+
+## Aggregation
+
+```nim
+echo ageCol.sumInt64()
+echo ageCol.avgInt64()
+echo ageCol.minInt64()
+echo ageCol.maxInt64()
+echo ageCol.count()
+```
+
+## Kodierung
+
+### RLE (Run-Length Encoding)
+
+```nim
+let rle = rleEncode(@[1'i64, 1, 1, 2, 2, 3])
+```
+
+### Dictionary-Kodierung
+
+```nim
+let dict = dictEncode(@["apple", "banana", "apple"])
+```
+
+## Spaltentypen
+
+| Typ | Beschreibung |
+|------|-------------|
+| `int32` | 32-Bit Integer |
+| `int64` | 64-Bit Integer |
+| `float32` | 32-Bit Float |
+| `float64` | 64-Bit Float |
+| `string` | Variable-length String |
+| `bool` | Boolean |
+
+## Anwendungsfälle
+
+- OLAP-Workloads
+- Großflächige Aggregation
+- Data Warehousing
+- Zeitreihenanalyse