fix: resolve .env.local not loading in docker compose

Fixes issue #1827 where Docker Compose wasn't properly loading .env.local file.

Problem:
- Docker Compose expects .env file for variable substitution but docs say to use .env.local
- This caused environment variables to not be loaded in Docker containers

Solution:
- Updated docker-compose.yaml to load both .env and .env.local files
- Created setup-env.sh script to help users sync .env.local to .env
- Updated documentation with clear instructions for Docker users
- Maintains backward compatibility with existing setups

Changes:
- Modified docker-compose.yaml to use array syntax for env_file
- Added scripts/setup-env.sh helper script
- Updated CONTRIBUTING.md and index.md documentation

This ensures environment variables work correctly in Docker while maintaining
the security best practice of using .env.local for sensitive data.

Contributed by: Keoma Wright

docs/docs/CONTRIBUTING.md

@@ -95,11 +95,20 @@ Interested in maintaining and growing the project? Fill out our [Contributor App
      OPENAI_API_KEY=XXX
      ...
      ```
-  3. Optionally set:
+  3. **For Docker users**: Run the setup script or manually copy `.env.local` to `.env`:
+     ```bash
+     # Option 1: Use the setup script
+     ./scripts/setup-env.sh
+     
+     # Option 2: Manual copy
+     cp .env.local .env
+     ```
+     Docker Compose requires `.env` for variable substitution.
+  4. Optionally set:
      - Debug level: `VITE_LOG_LEVEL=debug`
      - Context size: `DEFAULT_NUM_CTX=32768`
 
-**Note**: Never commit your `.env.local` file to version control. It’s already in `.gitignore`.
+**Note**: Never commit your `.env.local` or `.env` files to version control. They're already in `.gitignore`.
 
 ### 2️⃣ Run Development Server