refactor(config): Extract configuration into src/config/ module

- Create src/config/paths.js for all file paths and env vars
- Create src/config/site.js for site configuration loading
- Create src/config/index.js as unified config export
- Prepare for server.js modularization (Phase 2.1)

Part of deslopification roadmap: break 1997-line server.js into layers

dashcaddy-api/src/config/site.js

@@ -0,0 +1,79 @@
+/**
+ * Site configuration loader
+ * Loads and manages site-wide settings from config.json
+ */
+const fs = require('fs');
+const { validateConfig } = require('../../config-schema');
+const { CADDY } = require('../../constants');
+
+let siteConfig = {
+  tld: '.home',
+  caName: '',
+  dnsServerIp: '',
+  dnsServerPort: CADDY.DEFAULT_DNS_PORT,
+  dashboardHost: '',
+  timezone: 'UTC',
+  dnsServers: {},
+  configurationType: 'homelab',
+  domain: '',
+  routingMode: 'subdomain'
+};
+
+function loadSiteConfig(CONFIG_FILE, log) {
+  try {
+    if (fs.existsSync(CONFIG_FILE)) {
+      const raw = JSON.parse(fs.readFileSync(CONFIG_FILE, 'utf8'));
+
+      // Validate config and log any issues
+      const { valid, errors: configErrors, warnings: configWarnings } = validateConfig(raw);
+      if (log && log.warn) {
+        if (!valid) {
+          log.warn('config', 'Config validation errors', { errors: configErrors });
+        }
+        for (const w of configWarnings) {
+          log.warn('config', w);
+        }
+      }
+
+      siteConfig.tld = raw.tld || '.home';
+      if (!siteConfig.tld.startsWith('.')) siteConfig.tld = '.' + siteConfig.tld;
+      siteConfig.caName = raw.caName || '';
+      siteConfig.dnsServerIp = (raw.dns && raw.dns.ip) || '';
+      siteConfig.dnsServerPort = (raw.dns && raw.dns.port) || CADDY.DEFAULT_DNS_PORT;
+      siteConfig.dashboardHost = raw.dashboardHost || `status${siteConfig.tld}`;
+      siteConfig.timezone = raw.timezone || 'UTC';
+      siteConfig.dnsServers = raw.dnsServers || {};
+      siteConfig.configurationType = raw.configurationType || 'homelab';
+      siteConfig.domain = raw.domain || '';
+      siteConfig.routingMode = raw.routingMode || 'subdomain';
+      siteConfig.pylon = raw.pylon || null;
+    }
+  } catch (e) {
+    if (log && log.error) {
+      log.error('config', 'Failed to load site config', { error: e.message });
+    }
+  }
+}
+
+/** Build a domain from subdomain + configured TLD or public domain */
+function buildDomain(subdomain) {
+  if (siteConfig.configurationType === 'public' && siteConfig.domain) {
+    return `${subdomain}.${siteConfig.domain}`;
+  }
+  return `${subdomain}${siteConfig.tld}`;
+}
+
+/** Build full service URL (protocol + host + path) */
+function buildServiceUrl(subdomain) {
+  if (siteConfig.routingMode === 'subdirectory' && siteConfig.domain) {
+    return `https://${siteConfig.domain}/${subdomain}`;
+  }
+  return `https://${buildDomain(subdomain)}`;
+}
+
+module.exports = {
+  siteConfig,
+  loadSiteConfig,
+  buildDomain,
+  buildServiceUrl,
+};