fix(cloudflare): resolve vite plugin config once across call sites (#16868)

* fix(cloudflare): resolve vite plugin config once across call sites

User options like remoteBindings, inspectorPort, persistState, configPath,
and auxiliaryWorkers were silently dropped during astro preview because the
preview entrypoint only received the adapter-computed half of the config.
Resolve the full @cloudflare/vite-plugin config once at integration setup
time so every call site (dev/build, prerenderer, preview) spreads a single
merged object and cannot accidentally drop user options.

* test(cloudflare): add regression test for remoteBindings during astro preview

Verifies that astro preview honors remoteBindings: false when a wrangler
binding is flagged remote: true. Confirmed to fail before the fix in
b4946e29 — wrangler.maybeStartOrUpdateRemoteProxySession throws from the
@cloudflare/vite-plugin preview path because the option is dropped.

* chore: cleanup comments