chore: add Firebase Hosting config for season content delivery

firebase init hosting wired to project block-seasons, public dir = deploy.
Generated season payload (deploy/content/) and CLI cache (.firebase/) are
gitignored — content/ is the source of truth, regenerated by the deploy
script in docs/firebase-hosting-guide.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.firebaserc

@@ -0,0 +1,5 @@
+{
+  "projects": {
+    "default": "block-seasons"
+  }
+}