refactor(config): require explicit BZOD data directory

README.md

@@ -168,9 +168,10 @@ services:
       - "8654:8654"
 
     volumes:
-      - ./data:/app/data
+      - /var/lib/bzod/data:/app/data
 
     environment:
+      - NX9_BZOD_DATA_DIR=/app/data
       - RUST_LOG=info
 ```
 
@@ -182,6 +183,28 @@ docker compose up -d
 
 ---
 
+# Data Directory & Configuration Precedence
+
+BZOD requires an explicit physical data root. There is **no implicit `./data` fallback**.
+
+Precedence:
+1. **CLI `--data-dir`** (Highest)
+2. **`NX9_BZOD_DATA_DIR`** environment variable
+3. **`config.toml` / `bzod.toml` `data_dir`** setting
+4. **Configuration Error** if no data directory is configured.
+
+Examples:
+
+```bash
+# Via environment variable
+NX9_BZOD_DATA_DIR=/var/lib/bzod/data bzod serve
+
+# Via CLI argument
+bzod migrate --data-dir=/var/lib/bzod/data --dry-run
+```
+
+---
+
 # Native Installation
 
 Download the latest release.
@@ -202,16 +225,16 @@ bzod --help
 
 # Initialize
 
-Create the administrator.
+Create the administrator (specifying `--data-dir` or `NX9_BZOD_DATA_DIR`):
 
 ```bash
-bzod create-admin
+NX9_BZOD_DATA_DIR=/var/lib/bzod/data bzod create-admin
 ```
 
-Start the server.
+Start the server:
 
 ```bash
-bzod serve
+NX9_BZOD_DATA_DIR=/var/lib/bzod/data bzod serve
 ```
 
 Default server:
@@ -234,6 +257,7 @@ After=network.target
 
 [Service]
 
+Environment=NX9_BZOD_DATA_DIR=/var/lib/bzod/data
 ExecStart=/usr/local/bin/bzod serve
 
 Restart=always