Enhance user configuration management and logging

- Introduced user configuration command to set API key.
- Updated README and documentation for user config and logging paths.
- Refactored logging to support user-specific log files.
- Added tests for user configuration and logging behavior.

README.md

@@ -9,6 +9,7 @@ AI Nexus currently documents AWS Bedrock Converse API as the workaround while An
 ```powershell
 cd nexus-claude-api
 uv sync --extra dev
+uv run nexus-claude-api config set --api-key "your-nexus-api-key"
 uv run nexus-claude-api start --port 4141 --claude-code
 ```
 
@@ -32,11 +33,17 @@ The printed command ends with `claude --model <configured-model>` so the current
 Credential lookup order:
 
 1. `--api-key`
-2. local `nexus-claude-api.local.json`
+2. user config `~/.config/nexus-claude-api/config.json`
 3. `NEXUS_API_KEY`
 4. `AWS_BEARER_TOKEN_BEDROCK`
 
-For local hardcoded configuration, create `nexus-claude-api.local.json`:
+To write user config:
+
+```powershell
+nexus-claude-api config set --api-key "your-nexus-api-key"
+```
+
+This creates `~/.config/nexus-claude-api/config.json`:
 
 ```json
 {
@@ -44,7 +51,15 @@ For local hardcoded configuration, create `nexus-claude-api.local.json`:
 }
 ```
 
-This file is ignored by git.
+Logs are written to `~/.config/nexus-claude-api/logs/nexus-claude-api.log` by default.
+
+For repository-local development only, pass `--dev` and create `nexus-claude-api.local.json` in the current directory:
+
+```powershell
+uv run nexus-claude-api start --dev --port 4141 --claude-code
+```
+
+In development mode, config is read from `nexus-claude-api.local.json` and logs are written to `logs/nexus-claude-api.log` in the current directory. The local config file is ignored by git.
 
 The service binds to `127.0.0.1` by default and does not persist API keys.
 
@@ -53,3 +68,4 @@ The service binds to `127.0.0.1` by default and does not persist API keys.
 - [PRD](docs/PRD.md)
 - [Requirements Design](docs/REQUIREMENTS_DESIGN.md)
 - [AI Nexus Claude Documentation](docs/AI_NEXUS_CLAUDE.md)
+- [Python Internal Distribution Guide](docs/PACKAGING_DISTRIBUTION.md)