chore: move to Node 26 (#4295)

* chore: move to Node 26

Docker image and CI run on Node 26 (bookworm-slim, same Debian base as before).

Node 26's bundled undici reads the global dispatcher from the
`undici.globalDispatcher.2` slot, so the guard's 10-minute timeout wrap on
`.1` no longer reached plain fetch() and provider calls fell back to the
5-minute headers timeout. The guard now wraps every present slot and tracks
wrapped dispatchers in a set, since compose() can return a Proxy that writes
a marker property through to the original dispatcher.

* test(puter-js): disable Node's web storage in test workers

Node 26 defines its own localStorage global, undefined without a storage
file, and vitest's jsdom environment doesn't replace globals that already
exist, so jsdom tests saw localStorage as undefined.

.github/workflows/ai-provider-integration-tests.yaml

@@ -22,7 +22,7 @@ jobs:
             - name: Set up Node.js
               uses: actions/setup-node@v7
               with:
-                  node-version: '24'
+                  node-version: '26'
                   cache: 'npm'
 
             - name: Install dependencies

.github/workflows/backend-tests.yaml

@@ -57,7 +57,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies
@@ -88,7 +88,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies
@@ -154,7 +154,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies

.github/workflows/docs-build.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies

.github/workflows/puterjs-tests.yaml

@@ -57,7 +57,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies
@@ -78,7 +78,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies
@@ -135,7 +135,7 @@ jobs:
         if: needs.changes.outputs.puterjs == 'true'
         uses: actions/setup-node@v7
         with:
-          node-version: '24'
+          node-version: '26'
           cache: 'npm'
 
       - name: Install dependencies