feat(auth): extend refresh TTL and keep session on transient errors

Bumps refresh token lifetime to 720h with env overrides, and stops
clearing the local session for non-401 refresh failures so users aren't
logged out by transient network blips. Adds a 60s retry timer when a
refresh fails for non-auth reasons.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/shared/config/config_test.go

@@ -166,6 +166,33 @@ scheduler:
 	}
 }
 
+func TestLoadPrefersEnvJWTSettings(t *testing.T) {
+	t.Setenv("JWT_SECRET", "env-jwt-secret")
+	t.Setenv("JWT_ACCESS_TTL", "20m")
+	t.Setenv("JWT_REFRESH_TTL", "720h")
+
+	configPath := writeTestConfig(t, `
+jwt:
+  secret: config-jwt-secret
+  access_ttl: 15m
+  refresh_ttl: 168h
+`)
+
+	cfg, err := Load(configPath)
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if cfg.JWT.Secret != "env-jwt-secret" {
+		t.Fatalf("expected env jwt secret, got %q", cfg.JWT.Secret)
+	}
+	if cfg.JWT.AccessTTL != 20*time.Minute {
+		t.Fatalf("expected env jwt access ttl 20m, got %s", cfg.JWT.AccessTTL)
+	}
+	if cfg.JWT.RefreshTTL != 720*time.Hour {
+		t.Fatalf("expected env jwt refresh ttl 720h, got %s", cfg.JWT.RefreshTTL)
+	}
+}
+
 func TestLoadAppliesMembershipDefaults(t *testing.T) {
 	configPath := writeTestConfig(t, `
 membership: {}