[AZ-189] [AZ-190] [AZ-191] [AZ-192] [AZ-193] [AZ-194] [AZ-195] Add e2e blackbox test suite

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_docs/02_document/modules/common_extensions_stream_extensions.md

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+# Module: Azaion.Common.Extensions.StreamExtensions
+
+## Purpose
+Stream-to-string conversion utility.
+
+## Public Interface
+
+| Method | Signature | Description |
+|--------|-----------|-------------|
+| `ConvertToString` | `static string ConvertToString(this Stream stream)` | Reads entire stream as UTF-8 string, resets position to 0 afterward |
+
+## Internal Logic
+Resets stream position to 0, reads via `StreamReader`, then resets again so the stream remains usable.
+
+## Dependencies
+- `System.Text.Encoding`, `System.IO.StreamReader` (BCL only)
+
+## Consumers
+- `SecurityTest.EncryptDecryptTest` — converts decrypted stream to string for assertion
+
+## Data Models
+None.
+
+## Configuration
+None.
+
+## External Integrations
+None.
+
+## Security
+None.
+
+## Tests
+Indirectly tested via `SecurityTest.EncryptDecryptTest`.