phase-8: verify WASM engine build + in-browser sandbox complete

- WASM game engine (cmd/acb-wasm/) with loadState/step/runMatch API
- Pre-compiled 6 strategy bots to WASM (web/public/wasm/bots/)
- In-browser sandbox with Monaco editor (web/src/pages/sandbox.ts)
- WASM upload mode with interface validation
- Opponent selector (up to 3 opponents for 2-4 player matches)
- Replay viewer integration with fog-of-war toggle and view modes
- All tests pass, go vet clean, npm build succeeds

.needle-predispatch-sha

@@ -1 +1 @@
-164fcd225b8d5d0c6179bc1ea3c0ead92004efb3
+f0639a6e36c5252bf95380dc6c6117d389f6eaae