Add flexible configuration with custom file path support

\n- Add DLC_CONFIG_FILE environment variable for custom config paths\n- Update config.go to support both default and custom config file locations\n- Update README.md and AGENTS.md with configuration documentation\n- Remove /Users/gabrielradureau/.dancelessonscoach/ directory approach\n- Add os import to config.go\n- Test all configuration scenarios

AGENTS.md

@@ -141,7 +141,15 @@ go run cmd/server/main.go &
 
 **Configuration File Support:**
 
-A `config.example.yaml` file is provided as a template:
+A `config.example.yaml` file is provided as a template. By default, the application looks for `config.yaml` in the current working directory.
+
+To specify a custom config file path, set the `DLC_CONFIG_FILE` environment variable:
+
+```bash
+DLC_CONFIG_FILE="/path/to/config.yaml" go run ./cmd/server
+```
+
+Example `config.yaml`:
 
 ```yaml
 server:
@@ -153,10 +161,12 @@ shutdown:
 ```
 
 **Configuration Loading:**
-- Environment variables take precedence over defaults
+- **File-based configuration** takes highest precedence
+- **Environment variables** override defaults but are overridden by config file
+- **Default values** are used when no other configuration is provided
 - All configuration is validated on startup
 - Invalid configurations cause server startup failure
-- Configuration values are logged at startup
+- Configuration values and source are logged at startup
 
 **Verification:**
 ```bash