finish the main code

app/config.py

@@ -0,0 +1,40 @@
+"""
+app/config.py
+
+Central place for all runtime configuration.
+Values are read from environment variables, with sensible defaults.
+Nothing in this file imports from the rest of the project.
+"""
+
+import os
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class Config:
+    # Kubernetes connection
+    in_cluster: bool  # True when running as a pod inside k3s
+    kubeconfig: str  # path to kubeconfig file (ignored if in_cluster=True)
+
+    # Dashboard behaviour
+    cache_ttl: int  # seconds between Kubernetes API refreshes
+    page_title: str
+    page_icon: str
+
+    # Metrics
+    metrics_enabled: bool  # set False if metrics-server is not installed
+
+
+def load() -> Config:
+    """
+    Read config from the environment.
+    Call once at app startup — the result is immutable.
+    """
+    return Config(
+        in_cluster=os.getenv("IN_CLUSTER", "").lower() in ("1", "true", "yes"),
+        kubeconfig=os.getenv("KUBECONFIG", os.path.expanduser("~/.kube/config")),
+        cache_ttl=int(os.getenv("CACHE_TTL", "15")),
+        page_title=os.getenv("PAGE_TITLE", "k3s Dashboard"),
+        page_icon=os.getenv("PAGE_ICON", "☸️"),
+        metrics_enabled=os.getenv("METRICS_ENABLED", "true").lower() != "false",
+    )