Serve the same court twice, so staging can be tried before the crowd arrives

The image now answers at /staging/ as well as /, via an alias to the same
root — that way the staging deploy works whether or not Coolify strips the
path prefix, and the staging branch needs no diff of its own to merge.

The manifest MIME moved from an exact-match location into the stock types
map: an exact match would have missed the /staging/ copy, and a regex
location would have out-ranked the prefix and resolved against root.

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

HANDOFF.md

@@ -23,6 +23,11 @@ the primary target.
   a push. **Bump `main.js?v=N` in index.html every time** or phones keep the old build.
   The Dockerfile must also COPY any new top-level file (it currently ships `index.html`,
   `manifest.webmanifest`, `*.js`, `assets/`).
+- **Staging**: the `staging` branch deploys to splatter-tennis.wuwi.one/staging (own Coolify
+  resource, same repo, branch `staging`). Test there first, then merge to `main` for the testteam.
+  The branch carries NO diff against main — the image serves the app at both `/` and `/staging/`,
+  so it can be fast-forwarded and merged freely. Note it shares the origin (and therefore
+  localStorage) with prod.
 - **Oliver edits files himself** (tuning values, sometimes sprites). ALWAYS Read current file state
   before editing; never assume your last version is what is on disk.