feat: add shared project deployment with Dokploy project-level variables

- Add SHARED_PROJECT_ID and SHARED_ENVIRONMENT_ID to all docker-compose files
- Use Dokploy's project-level variable syntax: ${{project.VARIABLE}}
- Deploy all user AI stacks to a single shared Dokploy project
- Update DOKPLOY_DEPLOYMENT.md with shared project configuration guide
- Add comprehensive SHARED_PROJECT_DEPLOYMENT.md architecture documentation

Benefits:
- Centralized management (all stacks in one project)
- Resource efficiency (no per-user project overhead)
- Simplified configuration (project-level shared vars)
- Better organization (500 apps in 1 project vs 500 projects)

How it works:
1. Portal reads SHARED_PROJECT_ID from environment
2. Docker-compose uses ${{project.SHARED_PROJECT_ID}} to reference project-level vars
3. Dokploy resolves these at runtime
4. Portal deploys user stacks as applications within the shared project

Fallback: If variables not set, falls back to legacy behavior (separate project per user)

docs/DOKPLOY_DEPLOYMENT.md

@@ -91,6 +91,75 @@ main branch     → git.app.flexinit.nl/oussamadouhou/ai-stack-deployer:latest
 
 ---
 
+## Shared Project Configuration (IMPORTANT)
+
+### What is Shared Project Deployment?
+
+The portal deploys **all user AI stacks as applications within a single shared Dokploy project**, instead of creating a new project for each user. This provides:
+
+- ✅ Better organization (all stacks in one place)
+- ✅ Shared environment variables
+- ✅ Centralized monitoring
+- ✅ Easier management
+
+### How It Works
+
+```
+Dokploy Project: ai-stack-portal
+├── Environment: deployments
+│   ├── Application: john-dev
+│   ├── Application: jane-prod
+│   └── Application: alice-test
+```
+
+### Setting Up the Shared Project
+
+**Step 1: Create the Shared Project in Dokploy**
+
+1. In Dokploy UI, create a new project:
+   - Name: `ai-stack-portal` (or any name you prefer)
+   - Description: "Shared project for all user AI stacks"
+
+2. Note the **Project ID** (visible in URL or API response)
+   - Example: `2y2Glhz5Wy0dBNf6BOR_-`
+
+3. Get the **Environment ID**:
+   ```bash
+   curl -s "http://10.100.0.20:3000/api/project.one?projectId=2y2Glhz5Wy0dBNf6BOR_-" \
+     -H "Authorization: Bearer $DOKPLOY_API_TOKEN" | jq -r '.environments[0].id'
+   ```
+   - Example: `RqE9OFMdLwkzN7pif1xN8`
+
+**Step 2: Configure Project-Level Variables**
+
+In the shared project (`ai-stack-portal`), add these **project-level environment variables**:
+
+| Variable Name | Value | Purpose |
+|---------------|-------|---------|
+| `SHARED_PROJECT_ID` | `2y2Glhz5Wy0dBNf6BOR_-` | The project where user stacks deploy |
+| `SHARED_ENVIRONMENT_ID` | `RqE9OFMdLwkzN7pif1xN8` | The environment within that project |
+
+**Step 3: Reference Variables in Portal Applications**
+
+The portal's docker-compose files use Dokploy's variable syntax to reference these:
+
+```yaml
+environment:
+  - SHARED_PROJECT_ID=${{project.SHARED_PROJECT_ID}}
+  - SHARED_ENVIRONMENT_ID=${{project.SHARED_ENVIRONMENT_ID}}
+```
+
+**This syntax `${{project.VARIABLE}}` tells Dokploy**: "Get this value from the project-level environment variables"
+
+### Important Notes
+
+- ⚠️ **Both variables MUST be set** in the shared project for deployment to work
+- ⚠️ If not set, portal will fall back to creating separate projects per user (legacy behavior)
+- ✅ You can have different shared projects for dev/staging/prod environments
+- ✅ All 3 portal deployments (dev/staging/prod) should point to their respective shared projects
+
+---
+
 ## Setting Up Dokploy
 
 ### Step 1: Create Dev Application
@@ -107,12 +176,28 @@ main branch     → git.app.flexinit.nl/oussamadouhou/ai-stack-deployer:latest
    - Enable SSL (via Traefik wildcard cert)
 
 3. **Set Environment Variables**:
+   
+   **Important**: The portal application should be deployed **inside the shared project** (e.g., `ai-stack-portal-dev`).
+   
+   Then set these **project-level variables** in that shared project:
+   ```env
+   SHARED_PROJECT_ID=<your-shared-project-id>
+   SHARED_ENVIRONMENT_ID=<your-shared-environment-id>
+   ```
+   
+   And these **application-level variables** in the portal app:
    ```env
    DOKPLOY_URL=http://10.100.0.20:3000
    DOKPLOY_API_TOKEN=<your-token>
    STACK_DOMAIN_SUFFIX=ai.flexinit.nl
    STACK_IMAGE=git.app.flexinit.nl/flexinit/agent-stack:latest
    ```
+   
+   The docker-compose file will automatically reference the project-level variables using:
+   ```yaml
+   SHARED_PROJECT_ID=${{project.SHARED_PROJECT_ID}}
+   SHARED_ENVIRONMENT_ID=${{project.SHARED_ENVIRONMENT_ID}}
+   ```
 
 4. **Configure Webhook**:
    - Event: **Push**