ci: upgrade to Node 24, remove npm@11 global install

Node 24 ships with npm@11 built-in, fixing the broken `npm install -g
npm@11` on Node 22.22.2 runners. Also aligns with GitHub's upcoming
deprecation of Node 20 actions (June 2026).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jchris

.nvmrc

@@ -1 +1 @@
-lts/*
+24

actions/core-publish/action.yaml

@@ -8,7 +8,6 @@ runs:
       run: |
         rm -f ~/.npmrc
         find . \( -name .npmrc -o -name npmrc-smoke \) -print0 | xargs -0 rm -f --
-        npm install -g npm@11
         npm --version
         git fetch --tags --force > /dev/null 2>&1
         git checkout origin/main ./allowed_signers

actions/runtime/action.yaml

@@ -14,5 +14,5 @@ runs:
     #    - uses: useblacksmith/setup-node@v5
     - uses: actions/setup-node@v4
       with:
-        node-version: "22"
+        node-version: "24"
         cache: pnpm