chore: bump node floor to 20.19 (Node 18 EOL'd 2025-04)

Required to merge eslint 10 in PR #2 -- eslint 10 dropped Node 18.
Node 18 reached end-of-life a year ago; every actively maintained LTS
line (20, 22, 24) gets tested in CI. Users on Node 18 can stay on
claude-code-ssh 3.2.x.

Author: hunchom

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        node: [18, 20, 22]
+        node: [20, 22, 24]
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-node@v5

package.json

@@ -54,6 +54,6 @@
     "prettier": "^3.2.4"
   },
   "engines": {
-    "node": ">=18.0.0"
+    "node": ">=20.19.0"
   }
 }