frontend: Fix /auth proxy path for OIDC callback and enforce LF line endings

[jooskim]

Summary

Fix the local dev proxy so the OIDC login flow completes without 404s, and enforce LF line endings for TypeScript/JavaScript/JSON files.

Related Issue

N/A

Changes

• frontend/rsbuild.config.ts / frontend/vite.config.ts: Change the proxy key for the auth route from /auth to /auth/. /auth is a React route that the Go backend's /oidc-callback handler redirects users to after a successful OIDC login. Without the trailing slash, the dev proxy was matching /auth as a prefix path and forwarding it to the backend instead of serving the frontend bundle, resulting in 404s after the OIDC callback.
• .gitattributes: Add text eol=lf rules for *.ts, *.tsx, *.js, *.jsx, and *.json, matching the existing rule for *.go. This is to enforce consistent EOL rules across the entire stack.
• frontend/vite.config.ts: Convert from CRLF to LF to align with the new .gitattributes policy.

Steps to Test

1. Configure an OIDC provider in Headlamp and start the frontend dev server (npm run frontend).
2. Initiate the OIDC login flow.
3. Confirm the /oidc-callback redirect lands on the /auth React route without a 404.

Screenshots

OIDC callback ends up hitting 404s without /auth proxy prefix

Notes for the Reviewer

The root cause was that Vite and rsbuild both treat proxy keys without a trailing slash as exact-match routes, not prefix matches. Adding / makes them proxy only requests whose path starts with /auth/, leaving the bare /auth React route to be served by the dev server as intended.

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