feat(config): implement multi-tenant config system (DAW/furt#89)

- nginx-style furt.conf configuration
- Multi-tenant mail routing per API key
- Custom SMTP support per customer
- Backward compatibility via server.lua adapter

WIP: Ready for testing on werner

config/server.lua

@@ -1,25 +1,30 @@
 -- config/server.lua
--- Server configuration for Furt Lua HTTP-Server
+-- Multi-Tenant server configuration using nginx-style config parser
+-- Dragons@Work Digital Sovereignty Project
 
-return {
-    -- HTTP Server settings
-    host = "127.0.0.1",
-    port = 8080,
+local ConfigParser = require("src.config_parser")
 
-    -- Timeouts (seconds)
-    client_timeout = 10,
+-- Load configuration from furt.conf
+local config = ConfigParser.load_config()
+
+-- Add legacy compatibility and runtime enhancements
+local server_config = {
+    -- HTTP Server settings (from [server] section)
+    host = config.server.host,
+    port = config.server.port,
+
+    -- Timeouts and limits
+    client_timeout = config.server.client_timeout or 10,
 
     -- CORS Configuration
     cors = {
-        -- Default allowed origins for development
-        -- Override in production with CORS_ALLOWED_ORIGINS environment variable
         allowed_origins = (function()
             local env_origins = os.getenv("CORS_ALLOWED_ORIGINS")
             if env_origins then
                 -- Parse comma-separated list from environment
                 local origins = {}
                 for origin in env_origins:gmatch("([^,]+)") do
-                    table.insert(origins, origin:match("^%s*(.-)%s*$")) -- trim whitespace
+                    table.insert(origins, origin:match("^%s*(.-)%s*$"))
                 end
                 return origins
             else
@@ -35,54 +40,40 @@ return {
     },
 
     -- Logging
-    log_level = "info",
-    log_requests = true,
+    log_level = config.server.log_level or "info",
+    log_requests = config.server.log_requests or true,
 
-    -- API-Key-Authentifizierung (PRODUCTION READY)
-    api_keys = {
-        -- Hugo Frontend API-Key (für Website-Formulare)
-        [os.getenv("HUGO_API_KEY") or "hugo-dev-key-change-in-production"] = {
-            name = "Hugo Frontend",
-            permissions = {"mail:send"},
-            allowed_ips = {
-                "127.0.0.1",           -- Localhost
-                "10.0.0.0/8",          -- Private network
-                "192.168.0.0/16",      -- Private network
-                "172.16.0.0/12"        -- Private network
-            }
-        },
+    -- API Keys (converted from nginx-style to old format for backward compatibility)
+    api_keys = config.api_keys,
 
-        -- Admin API-Key (für Testing und Management)
-        [os.getenv("ADMIN_API_KEY") or "admin-dev-key-change-in-production"] = {
-            name = "Admin Access",
-            permissions = {"*"},  -- All permissions
-            allowed_ips = {
-                "127.0.0.1",           -- Local only for admin
-                "10.0.0.0/8"           -- Internal network
-            }
-        },
+    -- Default SMTP config (for legacy compatibility)
+    mail = config.smtp_default,
 
-        -- Optional: Monitoring API-Key (nur Health-Checks)
-        [os.getenv("MONITORING_API_KEY") or "monitoring-dev-key"] = {
-            name = "Monitoring Service",
-            permissions = {"monitoring:health"},
-            allowed_ips = {
-                "127.0.0.1",
-                "10.0.0.0/8",
-                "172.16.0.0/12"
-            }
-        }
-    },
+    -- Multi-tenant mail configuration function
+    get_mail_config_for_api_key = function(api_key)
+        return ConfigParser.get_mail_config_for_api_key(config, api_key)
+    end,
 
-    -- Mail configuration (for SMTP integration)
-    mail = {
-        smtp_server = os.getenv("SMTP_HOST") or "mail.example.org",
-        smtp_port = tonumber(os.getenv("SMTP_PORT")) or 465,
-        use_ssl = true,
-        username = os.getenv("SMTP_USERNAME"),
-        password = os.getenv("SMTP_PASSWORD"),
-        from_address = os.getenv("SMTP_FROM") or "noreply@example.org",
-        to_address = os.getenv("SMTP_TO") or "admin@example.org"
-    }
+    -- Raw config access (for advanced usage)
+    raw_config = config
 }
 
+-- Print configuration summary on load
+print("Furt Multi-Tenant Configuration Loaded:")
+print("  Server: " .. server_config.host .. ":" .. server_config.port)
+print("  Log Level: " .. server_config.log_level)
+print("  Default SMTP: " .. (config.smtp_default.host or "not configured"))
+
+local api_key_count = 0
+for key_name, key_config in pairs(config.api_keys) do
+    api_key_count = api_key_count + 1
+    local smtp_info = ""
+    if key_config.mail_smtp_host then
+        smtp_info = " (custom SMTP: " .. key_config.mail_smtp_host .. ")"
+    end
+    print("  API Key: " .. key_config.name .. " -> " .. key_config.mail_to .. smtp_info)
+end
+print("  Total API Keys: " .. api_key_count)
+
+return server_config
+