fix(app): clear composer text input upon sending on mobile (#3564)

* fix(app): clear mobile composer input on submit

Submitting a prompt on mobile failed to clear the native text input because EditingTextInput.replaceText previously only called setNativeProps({ text }), which is ignored on Fabric and PasteTextInput.

Fix this by:
- Delegating replaceText in EditingTextInputNative to inputRef.current.replaceText when available, clearing via clear() when text is empty, and falling back to setNativeProps.
- Patching @mattermost/react-native-paste-input to expose replaceText(text, selection) backed by native Commands.setTextAndSelection, updating clear() to use live event counts, and preventing useImperativeHandle closures over null refs during initial mount.
- Registering the patch in scripts/postinstall-patches.mjs and adding unit tests for native text input replacement and clearing.

* fix: update nix npm dependency hash

scripts/postinstall-patches.mjs

@@ -20,6 +20,10 @@ const patchedPackages = [
     nodeModulesPath: "node_modules/react-native-gesture-handler",
     patchPrefix: "react-native-gesture-handler+",
   },
+  {
+    nodeModulesPath: "node_modules/@mattermost/react-native-paste-input",
+    patchPrefix: "@mattermost+react-native-paste-input+",
+  },
   {
     nodeModulesPath: "packages/server/node_modules/@opencode-ai/sdk",
     patchPrefix: "@opencode-ai+sdk+",