Add Cloudflare Workers test support with Miniflare

Implement comprehensive test environment setup for Cloudflare Workers using
Miniflare, enabling cross-runtime testing compatibility.  Add new cfworkers
directory with client/server test infrastructure and update existing test
files to use fetch-mock for better portability.

Author: dahlia

.github/FUNDING.yaml

@@ -1,2 +1,2 @@
-open_collective: fedify
-github: dahlia
+open_collective: fedify
+github: dahlia

.github/workflows/ai-labeler.yaml

@@ -13,17 +13,17 @@ jobs:
       issues: write
       pull-requests: write
     steps:
-    - uses: actions/checkout@v4
-    - if: >-
-        github.event.action != 'labeled' ||
-        github.event.label.name == 'status/needs triage'
-      uses: jlowin/ai-labeler@v0.5.1
-      with:
-        include-repo-labels: true
-        openai-api-key: ${{ secrets.OPENAI_API_KEY }}
-    - if: >-
-        github.event.action == 'labeled' &&
-        github.event.label.name == 'status/needs triage'
-      uses: actions-ecosystem/action-remove-labels@v1
-      with:
-        labels: "status/needs triage"
+      - uses: actions/checkout@v4
+      - if: >-
+          github.event.action != 'labeled' ||
+          github.event.label.name == 'status/needs triage'
+        uses: jlowin/ai-labeler@v0.5.1
+        with:
+          include-repo-labels: true
+          openai-api-key: ${{ secrets.OPENAI_API_KEY }}
+      - if: >-
+          github.event.action == 'labeled' &&
+          github.event.label.name == 'status/needs triage'
+        uses: actions-ecosystem/action-remove-labels@v1
+        with:
+          labels: "status/needs triage"