fix[installer](proxy): added upgrade header so ws connections can math between frontend and backend

[AlexSanchez-bit]

No description provided.

[github-actions]

🛑 AI review — Engineer review required

This PR touches critical paths or introduces changes the model cannot judge with sufficient confidence. @Kbayero @osmontero please review.

🛑 architecture (gemini-3-flash-lite) — blocking — must fix before merge

Summary: Modification of installer templates affecting proxy configuration and WebSocket support.

• high installer/templates/proxy.go:1 — Changes to installer templates require Tier 3 review as they impact infrastructure deployment and potential backwards compatibility for existing proxy setups.

🛑 bugs (gemini-3-flash-lite) — blocking — must fix before merge

Summary: Duplicate map directive in Nginx configuration causes syntax error.

• high installer/templates/proxy.go:57 — The 'map' directive is defined twice in the same configuration block (lines 1-4 and 57-60). Nginx configuration files do not allow duplicate 'map' blocks at the same scope; this will cause the Nginx service to fail to start.

🛑 security (gemini-3-flash-lite) — blocking — must fix before merge

Summary: Modification of Nginx proxy configuration templates for the installer.

• medium installer/templates/proxy.go:1 — The PR modifies the Nginx proxy configuration template used by the installer. Changes to infrastructure-as-code templates that handle proxying and header forwarding are security-critical as they impact request routing and potential header injection/manipulation.

[utmstackprapprover]

Changes requested — AI review found blocking issues (high/critical, or engineer review required). See above.

[utmstackprapprover]

Changes requested — AI review found blocking issues (high/critical, or engineer review required). See above.