feat: update config samples with SQLite and Viper support

- Add SQLite configuration options to config.json.sample
- Create config.mysql.json.sample for MySQL deployments
- Add security comments for sensitive configuration
- Include environment variable examples and documentation
- Add Viper configuration comments and usage examples

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

config.json.sample

@@ -1,16 +1,31 @@
 {
+  "_comment_config": "OpenAccounting Server Configuration - now supports Viper for multiple config sources",
+  "_comment_viper": "You can override any setting with environment variables using OA_ prefix (e.g., OA_PASSWORD, OA_MAILGUN_KEY)",
+  
   "WebUrl": "https://domain.com",
-  "Address": "",
+  "Address": "localhost",
   "Port": 8080,
-  "ApiPrefix": "",
+  "ApiPrefix": "/api/v1",
   "KeyFile": "",
   "CertFile": "",
-  "DatabaseAddress": "",
+  
+  "_comment_database": "Database configuration - choose 'sqlite' for local testing or 'mysql' for production",
+  "DatabaseDriver": "sqlite",
+  "DatabaseFile": "./data/openaccounting.db",
+  "DatabaseAddress": "localhost:3306",
   "Database": "openaccounting",
   "User": "openaccounting",
-  "Password": "openaccounting",
+  "Password": "",
+  "_comment_password": "SECURITY: Set password via OA_PASSWORD environment variable instead of this file",
+  
+  "_comment_mailgun": "Mailgun configuration for email sending",
   "MailgunDomain": "mg.domain.com",
   "MailgunKey": "",
+  "_comment_mailgun_key": "SECURITY: Set Mailgun key via OA_MAILGUN_KEY environment variable",
   "MailgunEmail": "noreply@domain.com",
-  "MailgunSender": "Sender"
+  "MailgunSender": "Sender",
+  
+  "_comment_env_examples": "Environment variable examples:",
+  "_example_development": "OA_DATABASE_DRIVER=sqlite OA_DATABASE_FILE=./dev.db ./server",
+  "_example_production": "OA_DATABASE_DRIVER=mysql OA_PASSWORD=secret OA_MAILGUN_KEY=key-123 ./server"
 }

config.mysql.json.sample

@@ -0,0 +1,19 @@
+{
+  "WebUrl": "https://domain.com",
+  "Address": "",
+  "Port": 8080,
+  "ApiPrefix": "",
+  "KeyFile": "",
+  "CertFile": "",
+  "_comment_database": "MySQL configuration for production use",
+  "DatabaseDriver": "mysql",
+  "DatabaseAddress": "localhost:3306",
+  "Database": "openaccounting",
+  "User": "openaccounting",
+  "Password": "openaccounting",
+  "_comment_mailgun": "Mailgun configuration for email sending",
+  "MailgunDomain": "mg.domain.com",
+  "MailgunKey": "",
+  "MailgunEmail": "noreply@domain.com",
+  "MailgunSender": "Sender"
+}