feat(redis): configure value preview limit (#12089)

* feat(redis): configure value preview limit

* docs(testing): record Redis preview limit verification

* refactor(redis): move preview limit to connection advanced settings

* docs(testing): update Redis advanced setting screenshot

* refactor(redis): place preview limit at bottom of advanced settings

docs/testing/redis-value-preview-11326.md

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+# Configurable Redis value preview limit (#11326)
+
+Verified on macOS 26.3 with the local DBX Web build on 2026-10-14.
+
+The new setting is at the bottom of **Redis connection → Advanced settings**. It is stored globally and applies to every Redis connection. It defaults to 64 KiB and
+accepts 1–65536 KiB. The selected value is passed to the Redis String/Bitmap
+preview request; complete downloads still use the raw-value endpoint.
+
+![Redis preview setting set to 256 KiB](assets/redis-value-preview-11326/setting-256-kib.png)
+
+## Manual Web verification
+
+A local Redis 7.4.9 server was seeded with these values:
+
+- a 101,084 byte JSON document containing 850 items and a final `END-11326` marker;
+- a 131,072 byte binary value containing every byte from 0 through 255 repeatedly;
+- a 5 byte value;
+- a 65,536 byte boundary value.
+
+With the default 64 KiB setting, the 101,084 byte JSON appeared as a read-only
+preview with the message that only 64 KiB was loaded. After changing the setting
+to 256 KiB and applying it, the open detail automatically refreshed: the full
+JSON became editable, the truncation notice disappeared, and the final items
+and `END-11326` marker were visible. Reloading the Web app preserved 256 KiB and
+opening the same key again kept the full editable value.
+
+![Full value after reload with 256 KiB persisted](assets/redis-value-preview-11326/persisted-full-value.png)
+
+## Automated verification
+
+- 187 `dbx-driver-redis` unit tests passed.
+- The ignored integration test against the local Redis server passed for text,
+  UTF-8 Chinese content, and binary data: 64 KiB truncation, 256 KiB complete
+  reads, exact-boundary reads, and complete raw downloads all preserved bytes.
+- 470 frontend tests passed across 23 focused suites, including Redis viewer behavior, settings apply and reset, settings transfer validation, and HTTP/Tauri argument forwarding.
+- Frontend formatting, lint, typecheck, and the Web backend build passed.
+- Invalid preview sizes below 1 KiB and above 64 MiB were rejected before Redis
+  I/O.