feat: add OPENCODE_CONFIG_DIR environment variable support (#629)

- Add env var check to getCliConfigDir() for config directory override
- Update detectExistingConfigDir() to include env var path in locations
- Add comprehensive tests (7 test cases)
- Document in README

Closes #627

README.md

@@ -135,6 +135,7 @@ No stupid token consumption massive subagents here. No bloat tools here.
     - [MCPs](#mcps)
     - [LSP](#lsp)
     - [Experimental](#experimental)
+    - [Environment Variables](#environment-variables)
   - [Author's Note](#authors-note)
   - [Warnings](#warnings)
   - [Loved by professionals at](#loved-by-professionals-at)
@@ -1181,6 +1182,12 @@ Opt-in experimental features that may change or be removed in future versions. U
 
 **Warning**: These features are experimental and may cause unexpected behavior. Enable only if you understand the implications.
 
+### Environment Variables
+
+| Variable | Description |
+|----------|-------------|
+| `OPENCODE_CONFIG_DIR` | Override the OpenCode configuration directory. Useful for profile isolation with tools like [OCX](https://github.com/kdcokenny/ocx) ghost mode. |
+
 
 ## Author's Note