fix: address PR review feedback and fix CI test failures

- Revert default transport to streamable-http (not a breaking change)
- Extract AVAILABLE_APPS constant to server/__init__.py (DRY)
- Wrap get_stdio_mcp ValueError in click.ClickException for clean errors
- Fix test_stdio.py: call _reload_config() so dynaconf sees env changes
- Use lazy %-style logging in stdio.py
- Add private API comments in test assertions
- Derive --enable-app CLI choices from AVAILABLE_APPS
- README: show explicit --transport stdio in uvx examples

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -23,7 +23,7 @@ Run the server locally with [uvx](https://docs.astral.sh/uv/) (no installation r
 NEXTCLOUD_HOST=https://your.nextcloud.instance.com \
 NEXTCLOUD_USERNAME=your_username \
 NEXTCLOUD_PASSWORD=your_app_password \
-  uvx nextcloud-mcp-server run
+  uvx nextcloud-mcp-server run --transport stdio
 ```
 
 Or add it directly to your MCP client configuration (e.g. `claude_desktop_config.json` or `.claude/settings.json`):
@@ -33,7 +33,7 @@ Or add it directly to your MCP client configuration (e.g. `claude_desktop_config
   "mcpServers": {
     "nextcloud": {
       "command": "uvx",
-      "args": ["nextcloud-mcp-server", "run"],
+      "args": ["nextcloud-mcp-server", "run", "--transport", "stdio"],
       "env": {
         "NEXTCLOUD_HOST": "https://your.nextcloud.instance.com",
         "NEXTCLOUD_USERNAME": "your_username",