refactor(config): require explicit BZOD data directory

docs/CLI.md

@@ -284,3 +284,27 @@ bzod doctor
 * SECURITY.md
 * API.md
 * ARCHITECTURE.md
+
+---
+
+# Data Directory Configuration
+
+BZOD requires an explicit physical data directory root. There is **no implicit `./data` fallback**.
+
+### Configuration Precedence
+
+1. **CLI `--data-dir`** (Highest priority)
+   ```bash
+   bzod serve --data-dir /var/lib/bzod/data
+   bzod migrate --data-dir=/var/lib/bzod/data --dry-run
+   ```
+2. **Environment Variable `NX9_BZOD_DATA_DIR`**
+   ```bash
+   export NX9_BZOD_DATA_DIR=/var/lib/bzod/data
+   bzod serve
+   ```
+3. **Configuration File (`bzod.toml` / `config.toml`)**
+   ```toml
+   data_dir = "/var/lib/bzod/data"
+   ```
+4. **Error**: If no data directory is provided via CLI, `NX9_BZOD_DATA_DIR`, or config file, BZOD terminates with an actionable error.