feat(cala): Phase 5 — browser app scaffold + four-worker runtime

.prettierignore

@@ -3,6 +3,8 @@ apps/*/dist/
 packages/*/dist/
 crates/solver/pkg/
 crates/solver/target/
+crates/cala-core/pkg/
+crates/cala-core/target/
 .planning/
 package-lock.json
 python/.venv/

apps/cala/README.md

@@ -0,0 +1,62 @@
+# CaLa
+
+Streaming calcium imaging demixing. Browser-native OMF pipeline port of Raymond Chang's [`cala`](https://github.com/raymondchang-ucla/cala) reference — streaming preprocess + fit + extend loops, backed by the Rust numerical core in `crates/cala-core`.
+
+## Status
+
+**Phase 5 exit complete, 2026-04-18.** End-to-end W1→W2→W4 pipeline runs on a real uncompressed 8-bit miniscope AVI. The production runtime is browser-only; see `.planning/CALA_DESIGN.md` for the full phase ledger and what's deferred to Phase 6+.
+
+## Dev
+
+```
+npm run dev -w apps/cala        # starts Vite with COOP/COEP headers set
+npm run verify-sab -w apps/cala # boots Vite, asserts SAB headers live
+npm run test:e2e -w apps/cala   # Phase 5 exit E2E on a real AVI fixture
+npm run test:e2e:cala           # same, from repo root
+```
+
+The E2E fixture lives under `.test_data/` (gitignored — local-only). The Phase 5 exit spec reads `.test_data/anchor_v12_prepped.avi` by default; if you don't have that file the test throws with a clear message. See `apps/cala/e2e/phase5-exit.e2e.test.ts` for the full harness — it pipes real AVI bytes through the real W1, W2, and W4 worker modules wired by the real SAB channel, with the WASM numerical core stubbed (Rust/WASM correctness is covered by the Phase 3 exit in `crates/cala-core`).
+
+`SharedArrayBuffer` (used by the worker runtime for SAB-backed channels, mutation queue, and event bus) needs cross-origin isolation:
+
+- `Cross-Origin-Opener-Policy: same-origin`
+- `Cross-Origin-Embedder-Policy: require-corp`
+
+The Vite dev server and preview server set these headers via `vite.config.ts`. If `SharedArrayBuffer` is undefined in the page, inspect response headers — the most common cause is serving through a proxy that strips them.
+
+## Production deploy (GitHub Pages)
+
+GitHub Pages does not support custom response headers. That means **`SharedArrayBuffer` won't work on the production Pages deploy as-is**. Two paths are available when the app goes live:
+
+1. **Cross-origin-isolation service worker** (`coi-serviceworker` pattern) — the service worker intercepts `fetch` and injects the COOP/COEP headers. Works on GitHub Pages without host changes. Planned for Phase 6+ when SAB-using UI code actually ships to production.
+2. **Alternative host** (Netlify, Cloudflare Pages) that honors a `_headers` file or equivalent. Requires deployment pipeline changes in `scripts/combine-dist.mjs` + `.github/workflows/deploy.yml`.
+
+Phase 5 exit (task 25) only requires local dev to work end-to-end. The production SAB story is a separate deliverable that doesn't block Phase 5.
+
+## Layout
+
+```
+apps/cala/
+├── index.html
+├── package.json           # @calab/* workspace deps
+├── vite.config.ts         # path aliases, WASM plugin, COOP/COEP headers
+├── tsconfig.json
+├── scripts/
+│   └── verify-sab.mjs     # smoke check for COOP/COEP header delivery
+└── src/
+    ├── App.tsx            # placeholder shell — components land in tasks 20-24
+    ├── index.tsx
+    ├── styles/global.css
+    └── vite-env.d.ts
+```
+
+Per-task layout expansions:
+
+| Task | Adds                                                                                                                 |
+| ---- | -------------------------------------------------------------------------------------------------------------------- |
+| 20   | `lib/data-store.ts`, `lib/run-control.ts`, `components/layout/ImportOverlay.tsx`, `components/layout/CaLaHeader.tsx` |
+| 21   | `workers/decode-preprocess.worker.ts`                                                                                |
+| 22   | `workers/fit.worker.ts`                                                                                              |
+| 23   | `workers/extend.worker.ts`, `workers/archive.worker.ts`                                                              |
+| 24   | `components/frame/SingleFrameViewer.tsx`, `lib/archive-client.ts`, `lib/dashboard-store.ts`                          |
+| 25   | `e2e/phase5-exit.e2e.test.ts`, `vitest.e2e.config.ts`, `test:e2e` scripts                                            |