refactor(browser): split browser cores via build ARG, add core selector (#237)

* refactor(browser): split browser cores via build ARG, add core selector

- Replace playwright official image with ubuntu:noble base in both
  docker/Dockerfile.browser and devenv/Dockerfile.browser; install
  browsers at build time driven by ARG/ENV BROWSER_CORES
- Add GET /cores endpoint to Browser Gateway reporting available cores
- Proxy GET /browser-contexts/cores in Go handler to Browser Gateway
- Add `core` field to BrowserContextConfigModel and GatewayBrowserContext;
  context creation selects the appropriate browser instance by core
- Frontend context-setting page fetches available cores and renders a
  core selector; saves core as part of the config JSON
- install.sh prompts for browser core selection and writes BROWSER_CORES
  to .env; builds the browser image locally before docker compose up
- Regenerate OpenAPI spec and TypeScript SDK

* fix: lint

docker/Dockerfile.browser

@@ -15,7 +15,10 @@ COPY apps/browser/ ./apps/browser/
 
 RUN cd apps/browser && bun run build
 
-FROM mcr.microsoft.com/playwright:v1.50.0-noble
+FROM ubuntu:noble
+
+ARG BROWSER_CORES=chromium,firefox
+ENV BROWSER_CORES=$BROWSER_CORES
 
 WORKDIR /app
 
@@ -29,7 +32,9 @@ COPY --from=builder /build/apps/browser/node_modules /app/node_modules
 COPY --from=builder /build/apps/browser/package.json /app/package.json
 COPY --from=builder /build/node_modules /node_modules
 
-RUN npx playwright install --with-deps chromium
+RUN for core in $(echo "$BROWSER_CORES" | tr ',' ' '); do \
+      bun /app/node_modules/.bin/playwright install --with-deps "$core"; \
+    done
 
 EXPOSE 8083