Move CI, the image and the Node types to 26 together

Three pins and a types package all described Node 22, and moving any one
of them alone puts the build somewhere the others are not: @types/node
on its own would typecheck against APIs the runtime does not have, and
the base image on its own would ship a major CI never exercised. So
ci.yml, publish.yml, release.yml, both Dockerfile stages and
@types/node move in one change.

Worth knowing before this is deployed: 26 is Current, not LTS. node:26-
alpine reports lts=none, where 24-alpine is Krypton and the 22-alpine we
are leaving is Jod. 26 is due to become Active LTS in October. Nothing
here needs 26 over 24 -- the pins are a single number if the LTS line is
preferred.

engines stays at >=20.19, which is the floor for running ihasmail rather
than the version we build it on; the README's recommendation follows CI
to 26.

Checked on the runtime, not just in CI: the image builds on 26-alpine,
starts, and answers /api/health, and the login, SSE and body-carrying
POST checks from the node-server upgrade pass against a server on
26.8.1.

package-lock.json

@@ -968,13 +968,13 @@
       "license": "MIT"
     },
     "node_modules/@types/node": {
-      "version": "22.20.2",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-22.20.2.tgz",
-      "integrity": "sha512-xlvWf4Vs9n1PEVYwP1n4vvG07M6y8WgvJ2t0vbrWTmijsIHp1cS+uJ2kMIRdY3nHZK0nCYKrPeD171+SzF4/zw==",
+      "version": "26.5.1",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-26.5.1.tgz",
+      "integrity": "sha512-CzNm2FezW4VR/LjG6yUdiEgLE/rAQ9Slj5gCu/C2VrdcW7I0ahNZ8DRbHT7zOZ6r3ONgd/bsQIeSaoDGrd1C6g==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
-        "undici-types": "~6.21.0"
+        "undici-types": "~8.9.0"
       }
     },
     "node_modules/@types/react": {
@@ -2778,9 +2778,9 @@
       }
     },
     "node_modules/undici-types": {
-      "version": "6.21.0",
-      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
-      "integrity": "sha512-iwDZqg0QAGrg9Rav5H4n0M64c3mkR59cJ6wQp+7C4nI0gsmExaedaYLNO44eT4AtBBwjbTiGPMlt2Md0T9H9JQ==",
+      "version": "8.9.0",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-8.9.0.tgz",
+      "integrity": "sha512-KTDyRTYX8sWmKXAikPHHSyc63CRPETMctyjKFupcC6OBLXT3xsN0e9aF7m+mIXutFWpUXuedtowG7iLOzp0kQg==",
       "dev": true,
       "license": "MIT"
     },
@@ -3186,7 +3186,7 @@
         "hono": "^4.13.7"
       },
       "devDependencies": {
-        "@types/node": "^22.13.10",
+        "@types/node": "^26.5.1",
         "tsx": "^4.23.13",
         "typescript": "^7.0.2"
       }