build: optimize Docker setup for Caddy SPA and improve runtime stability

Updated Dockerfile to streamline the hybrid build process and optimize artifact integration. Modified Caddyfile for better routing logic, enhanced security headers, Prometheus metrics, and improved API proxy handling. Adjusted `dc-gui.yaml` for container stability and simplified runtime configuration for `apiBaseUrl`. Expanded documentation with troubleshooting and session logs.

config/docker/caddy/web-app/Caddyfile

@@ -1,41 +1,69 @@
-:4000 {
-    # Root directory for static files
-    root * /usr/share/caddy
-
-    # Enable Gzip/Zstd compression
-    encode gzip zstd
-
-    # Serve static files
-    file_server
-
-    # Templates for runtime configuration (config.json)
-    templates {
-        mime application/json
-    }
-
-    # SPA Routing: Fallback to index.html for non-existent files
-    try_files {path} /index.html
-
-    # Cache Control for static assets (immutable)
-    @static {
-        file
-        path *.js *.css *.png *.jpg *.svg *.wasm
-    }
-    header @static Cache-Control "public, max-age=31536000, immutable"
-
-    # Security Headers (Future Proofing for Wasm)
-    header {
-        # Cross-Origin Isolation for SharedArrayBuffer (required for some Wasm features)
-        Cross-Origin-Opener-Policy "same-origin"
-        Cross-Origin-Embedder-Policy "require-corp"
-
-        # Standard Security Headers
-        X-Content-Type-Options "nosniff"
-        X-Frame-Options "DENY"
-    }
-
-    # Health Check
-    handle /health {
-        respond "healthy" 200
-    }
+{
+# Global Options
+# Enable Prometheus metrics
+  servers {
+            metrics
+          }
+}
+
+:4000 {
+# Root directory for static files
+  root * /usr/share/caddy
+
+# Access Logs (JSON format for Docker)
+  log {
+        output stdout
+        format json
+      }
+
+# Enable Gzip/Zstd compression
+  encode gzip zstd
+
+# Templates for runtime configuration (config.json)
+  templates {
+              mime application/json
+            }
+
+# Cache Control for static assets (immutable)
+  @static {
+            file
+            path *.js *.css *.png *.jpg *.svg *.wasm
+          }
+  header @static Cache-Control "public, max-age=31536000, immutable"
+
+# Security Headers (Future Proofing for Wasm)
+  header {
+         # Cross-Origin Isolation for SharedArrayBuffer (required for some Wasm features)
+           Cross-Origin-Opener-Policy "same-origin"
+           Cross-Origin-Embedder-Policy "require-corp"
+
+         # Standard Security Headers
+           X-Content-Type-Options "nosniff"
+           X-Frame-Options "DENY"
+           Referrer-Policy "strict-origin-when-cross-origin"
+           Permissions-Policy "camera=(), microphone=(), geolocation=()"
+         }
+
+# --- ROUTING LOGIC ---
+
+# 1. API Proxy (Priority 1)
+  handle /api/* {
+                  reverse_proxy api-gateway:8081 {
+                                                   header_up Host {upstream_hostport}
+                                                 }
+                }
+
+# 2. Health Check
+  handle /health {
+                   respond "healthy" 200
+                 }
+
+# 3. Static Files & SPA Fallback (Priority 2)
+  handle {
+         # Serve static files if they exist
+           file_server
+
+         # SPA Routing: Fallback to index.html for non-existent files
+           try_files {path} /index.html
+         }
 }

config/docker/caddy/web-app/Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1.8
 # ===================================================================
-# Dockerfile for Meldestelle Web-App (Pre-built Artifacts)
-# Version: 3.1.0 - Local Build Injection
+# Dockerfile for Meldestelle Web-App (Hybrid Build)
+# Version: 3.2.0 - Optimized & Cleaned
 # ===================================================================
 
 # === GLOBAL ARGS ===
@@ -31,6 +31,7 @@ COPY config/docker/caddy/web-app/config.json /usr/share/caddy/config.json
 COPY frontend/shells/meldestelle-portal/build/dist/js/productionExecutable/ /usr/share/caddy/
 
 # Ensure favicon exists (fallback)
+# Using the shared asset from existing config structure
 COPY config/docker/nginx/web-app/favicon.svg /usr/share/caddy/favicon.svg
 
 EXPOSE 4000

config/docker/caddy/web-app/config.json

@@ -1,3 +1,3 @@
 {
-  "apiBaseUrl": "{{env "API_BASE_URL" | default "http://localhost:8081"}}"
+  "apiBaseUrl": "{{env "API_BASE_URL" | default ""}}"
 }