chore: add cf.add and cf.addnx docs

docs/command-reference/cuckoo-filter/cf.add.md

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+---
+description: Learn how to use the CF.ADD command to add an item to a Cuckoo filter in Dragonfly.
+---
+import PageTitle from '@site/src/components/PageTitle';
+
+# CF.ADD
+
+<PageTitle title="Redis CF.ADD Command (Documentation) | Dragonfly" />
+
+## Syntax
+
+    CF.ADD key item
+
+**Time complexity:** O(k + i), where k is the number of sub-filters and i is `MAXITERATIONS`
+
+**ACL categories:** @cuckoo
+
+Adds a single `item` to the Cuckoo filter at `key`.
+If `key` does not exist, a new filter is created with default parameters.
+
+Unlike [`CF.ADDNX`](./cf.addnx.md), duplicate insertions are allowed — the same item can be added multiple times and will occupy a separate slot each time.
+Use `CF.DEL` once per insertion to remove it.
+
+If the filter is full and expansion is disabled (`EXPANSION 0`), an error is returned.
+
+## Return
+
+[Integer reply](https://valkey.io/topics/protocol/#integers):
+
+- `1` if the item was successfully added.
+- `0` if the filter is full and could not be expanded.
+
+## Examples
+
+```shell
+dragonfly> CF.ADD cf Hello
+(integer) 1
+
+dragonfly> CF.ADD cf Hello
+(integer) 1
+
+dragonfly> CF.COUNT cf Hello
+(integer) 2
+```
+
+## See also
+
+[`CF.ADDNX`](./cf.addnx.md) | [`CF.RESERVE`](./cf.reserve.md)

docs/command-reference/cuckoo-filter/cf.addnx.md

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+---
+description: Learn how to use the CF.ADDNX command to add an item to a Cuckoo filter only if it does not already exist.
+---
+import PageTitle from '@site/src/components/PageTitle';
+
+# CF.ADDNX
+
+<PageTitle title="Redis CF.ADDNX Command (Documentation) | Dragonfly" />
+
+## Syntax
+
+    CF.ADDNX key item
+
+**Time complexity:** O(k + i), where k is the number of sub-filters and i is `MAXITERATIONS`
+
+**ACL categories:** @cuckoo
+
+Adds a single `item` to the Cuckoo filter at `key` only if it does not already exist.
+If `key` does not exist, a new filter is created with default parameters.
+
+Unlike [`CF.ADD`](./cf.add.md), this command checks for the item before inserting.
+Because Cuckoo filters can return false positives, `CF.ADDNX` may decline to insert
+an item that was never actually added.
+
+If the filter is full and expansion is disabled (`EXPANSION 0`), an error is returned.
+
+## Return
+
+[Integer reply](https://valkey.io/topics/protocol/#integers):
+
+- `1` if the item was successfully added.
+- `0` if the item already exists in the filter (or is a false positive match).
+
+## Examples
+
+```shell
+dragonfly> CF.ADDNX cf Hello
+(integer) 1
+
+dragonfly> CF.ADDNX cf Hello
+(integer) 0
+
+dragonfly> CF.ADDNX cf World
+(integer) 1
+```
+
+## See also
+
+[`CF.ADD`](./cf.add.md) | [`CF.RESERVE`](./cf.reserve.md)