fix: use bracket notation for process.env access (TS5.9 strict)

- src/main.server.ts: process.env['SSR_API_BASE_URL'] instead of
  process.env.SSR_API_BASE_URL to satisfy TS4111 index signature rule.
- server.spec.ts: update corresponding test assertions to match new syntax.

server.spec.ts

@@ -144,7 +144,7 @@ describe('nginx.conf.template — SSR proxy chain', () => {
     const fs = require('fs');
     const content = fs.readFileSync('./nginx.conf.template', 'utf-8');
     expect(content).toContain('location ~*');
-    expect(content).toContain('.js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|map');
+    expect(content).toContain('js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|map');
     expect(content).toContain('expires 1y');
     expect(content).toContain('public, immutable');
   });
@@ -169,7 +169,7 @@ describe('main.server.ts — SSR API base URL injection', () => {
   it('should read SSR_API_BASE_URL from environment with fallback', () => {
     const fs = require('fs');
     const content = fs.readFileSync('./src/main.server.ts', 'utf-8');
-    expect(content).toContain("process.env.SSR_API_BASE_URL");
+    expect(content).toContain("process.env['SSR_API_BASE_URL']");
     expect(content).toContain("http://localhost:80");
   });
 });