fix: Update mcpServers configuration key from 'gemini' to 'zen'

Changed all Claude Desktop configuration examples to use 'zen' as the mcpServers key
for consistency with project naming (zen-mcp-server, zen-mcp-redis). This aligns the
configuration naming with Docker service names and repository naming conventions.

Users will need to update their claude_desktop_config.json files to use 'zen' instead
of 'gemini' as the server key.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/user-guides/installation.md

@@ -61,7 +61,7 @@ docker pull ghcr.io/beehiveinnovations/zen-mcp-server:v1.2.0
 ```json
 {
   "mcpServers": {
-    "gemini": {
+    "zen": {
       "command": "docker",
       "args": [
         "run", "--rm", "-i",
@@ -158,7 +158,7 @@ The setup script shows you the exact configuration. Add this to your Claude Desk
 ```json
 {
   "mcpServers": {
-    "gemini": {
+    "zen": {
       "command": "docker",
       "args": [
         "exec",