Update build configuration and improve token handling

- Change CI container image to debian:trixie-slim and set GOPROXY.
- Update Go version to 1.26 in Dockerfile and go.mod.
- Refactor token validation to use SHA-256 hashes instead of plain tokens.
- Add network policy to restrict access to the service.
- Enhance README with new configuration details and usage examples.
- Add tests for new token hash validation logic.

deploy/k3s/networkpolicy.yaml

@@ -0,0 +1,31 @@
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: gitea-mcp-auth-proxy-ingress
+  labels:
+    app: gitea-mcp-auth-proxy
+spec:
+  podSelector:
+    matchLabels:
+      app: gitea-mcp-auth-proxy
+  policyTypes:
+    - Ingress
+  ingress:
+    - from:
+        # Assumption: Traefik Pods run in namespace kube-system and expose label app.kubernetes.io/name=traefik.
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: kube-system
+          podSelector:
+            matchLabels:
+              app.kubernetes.io/name: traefik
+        # Assumption: Prometheus Pods run in namespace monitoring and expose label app.kubernetes.io/name=prometheus.
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: monitoring
+          podSelector:
+            matchLabels:
+              app.kubernetes.io/name: prometheus
+      ports:
+        - protocol: TCP
+          port: 8080