fix: OIDC env vars ignored when no oidc.enc file exists

When OIDC_* environment variables were set but no oidc.enc config file
existed, cfg.OIDC was nil and MergeFromEnv would silently return without
applying the env vars (due to nil receiver check).

Fix: Initialize cfg.OIDC to default values before merging env vars if
it's nil. This ensures OIDC can be configured purely through environment
variables without requiring a pre-existing config file.

Related to #853

internal/config/config.go

@@ -1163,6 +1163,10 @@ func Load() (*Config, error) {
 		oidcEnv["OIDC_CA_BUNDLE"] = val
 	}
 	if len(oidcEnv) > 0 {
+		// Ensure cfg.OIDC is initialized before merging env vars
+		if cfg.OIDC == nil {
+			cfg.OIDC = NewOIDCConfig()
+		}
 		cfg.OIDC.MergeFromEnv(oidcEnv)
 	}
 	if authUser := os.Getenv("PULSE_AUTH_USER"); authUser != "" {