fix: rsc react-server conditions and vite cors

[lazarv]

Fixes react-server based conditional import in the RSC layer.
Fixes Vite CORS handling.

[github-actions]

⚡ Benchmark Results

	PR 6e73bda	main 196ba2e
Config	50 connections, 10s/test	50 connections, 10s/test

Benchmark	Req/s	vs main	Avg Latency	vs main	P99 Latency	Throughput
minimal	1314	🟢 +10.8%	37.52 ms	🟢 -9.9%	84 ms	0.7 MB/s
small	1429	🟢 +9.5%	34.41 ms	🟢 -8.8%	60 ms	1.3 MB/s
medium	335	🔴 -1.5%	148.12 ms	🔴 +1.4%	222 ms	4.9 MB/s
large	29	🔴 -7.9%	1515.22 ms	🔴 +5.5%	2871 ms	2.9 MB/s
deep	913	🟢 +4.1%	54.16 ms	🟢 -4.0%	88 ms	3.0 MB/s
wide	43	⚪ -0.2%	1136.93 ms	🔴 +2.3%	2282 ms	2.3 MB/s
cached	3716	🟢 +1.5%	13.04 ms	⚪ -0.6%	26 ms	54.2 MB/s
client-min	997	🟢 +4.0%	49.59 ms	🟢 -3.5%	84 ms	2.5 MB/s
client-small	1008	🟢 +6.8%	49.04 ms	🟢 -6.3%	79 ms	2.9 MB/s
client-med	611	🟢 +19.8%	81.21 ms	🟢 -16.4%	134 ms	10.1 MB/s
client-large	98	🟢 +5.5%	504.8 ms	🟢 -2.5%	1014 ms	10.1 MB/s
client-deep	879	🟢 +8.4%	56.19 ms	🟢 -7.7%	86 ms	4.6 MB/s
client-wide	178	🟢 +3.7%	274.83 ms	🟢 -4.4%	449 ms	10.1 MB/s
static-json	7501	🔴 -3.3%	6.26 ms	🔴 +7.4%	15 ms	3.1 MB/s
static-js	7165	🔴 -3.8%	6.34 ms	🔴 +3.3%	16 ms	33.3 MB/s
404-miss	5254	🟢 +2.7%	9.05 ms	🟢 -1.3%	18 ms	0.6 MB/s

Legend

🟢 > 1% improvement | 🔴 > 1% regression | ⚪ within noise margin

Benchmarks run on GitHub Actions runners (shared infrastructure) — expect ~5% variance between runs. Consistent directional changes across multiple routes are more meaningful than any single number.