Add pr-number input to cloudflare-pages-preview actions

Both deploy and cleanup previously read context.payload.pull_request.number
directly, which throws on workflow_dispatch and other non-PR triggers.

New optional inputs:
- deploy: pr-number (default: event PR number), commit-sha (default: github.sha)
- cleanup: pr-number (default: event PR number)

If pr-number resolves to empty/0, the comment step is skipped gracefully
instead of crashing.

This lets /stageblog's companion workflow_dispatch receiver call the
composite deploy action directly instead of inlining wrangler + noindex
injection. The noindex logic staying in the actions repo (rather than in
a script file inside the caller repo that gets checked out at the fork's
SHA) is also the secure path — fork authors can't tamper with it.

The slash-commands README example is updated to use the deploy action
with the new inputs. The earlier commit on this branch (which rewrote
the example to call wrangler directly) is effectively superseded.

cloudflare-pages-preview/cleanup/action.yml

@@ -26,6 +26,13 @@ inputs:
     description: GitHub token for updating the PR comment
     required: false
     default: ${{ github.token }}
+  pr-number:
+    description: >-
+      PR number to update the sticky comment on. Only needed on triggers
+      where context.payload.pull_request is unavailable (e.g. workflow_dispatch).
+      Defaults to the event payload's PR number.
+    required: false
+    default: ${{ github.event.pull_request.number }}
 
 runs:
   using: composite
@@ -65,11 +72,16 @@ runs:
       uses: actions/github-script@v8
       env:
         COMMENT_MARKER: ${{ inputs.comment-marker }}
+        PR_NUMBER: ${{ inputs.pr-number }}
       with:
         github-token: ${{ inputs.github-token }}
         script: |
           const { owner, repo } = context.repo;
-          const prNumber = context.payload.pull_request.number;
+          const prNumber = Number(process.env.PR_NUMBER);
+          if (!prNumber) {
+            core.info('No PR number available — skipping comment update.');
+            return;
+          }
           const marker = process.env.COMMENT_MARKER;
 
           const { data: comments } = await github.rest.issues.listComments({