Inject MAP_TILE_URL into window.__ENV__ via html.tags + Docker build-arg

http://flights-ui.devwebzavod.ru/ru/flights-map was still hitting the
same-origin tile path after adding the k8s env: Modern.js renders the
<Suspense> fallback on the server (i18n isn't preloaded), so the route
component that reads getEnv() never actually runs during SSR. The page
hydrates client-side, where process.env is Rspack's empty stub and
MAP_TILE_URL is never set — getEnv() falls back to the default.

Move the value into window.__ENV__ instead:

- modern.config.ts: inline a <script> into html.tags that sets
  window.__ENV__ = { MAP_TILE_URL: <value> } at SSR-server startup.
  The snippet is authored once at server boot, so the HTML template
  baked into dist/standalone/html/main/index.html always carries the
  pod's tile URL.
- src/env/index.ts: merge window.__ENV__ on top of process.env so the
  browser prefers the injected value (process.env only has NODE_ENV
  after Rspack's polyfill).
- Dockerfile.react: accept MAP_TILE_URL as a build ARG and expose it
  as ENV before `pnpm build:standalone`, so Modern.js picks it up when
  building the HTML template. k8s env still flows into the Node SSR
  process; the build-arg path guarantees correctness even when the
  runtime env is stripped.
- deployment/build-docker.sh: forward MAP_TILE_URL through as a
  build-arg (default keeps the same-origin path). CI on the
  devwebzavod cluster can export MAP_TILE_URL=https://flights.test.aeroflot.ru/map/api/tile/{z}/{x}/{y}.jpeg
  before running build-docker.sh and the resulting image will serve
  tiles from the upstream the real Aeroflot ingress terminates.

Dockerfile.react

@@ -20,6 +20,13 @@ COPY src/ src/
 # broken backgrounds, missing tile icons).
 COPY config/ config/
 
+# Runtime-tunable env vars. modern.config.ts reads these when Modern.js
+# boots the SSR server at container start, so values set via k8s env
+# propagate without a rebuild. The ARG line lets CI also bake a value
+# into the image if the cluster can't set env at runtime.
+ARG MAP_TILE_URL
+ENV MAP_TILE_URL=${MAP_TILE_URL}
+
 RUN pnpm build:standalone
 
 FROM node:24-slim AS runtime