Simplify documentation and remove legacy migration scripts

- Remove migrate_add_combined_plans.py (schema now in database.py)
- Remove migrate_add_hsa_plan_type.py (schema now in database.py)
- Remove app/migrations/001_add_oidc_fields.py (schema now in database.py)
- Remove OIDC_IMPLEMENTATION_SUMMARY.md (development artifact)
- Simplify README.md: clearer structure, links to DOCKER.md, OIDC_SETUP.md, SECURITY.md
- Update OIDC_SETUP.md: remove migration step (handled automatically)

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

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: JavaDogWebDesign

OIDC_IMPLEMENTATION_SUMMARY.md

@@ -43,12 +43,7 @@ The HSA/FSA Tracker supports OpenID Connect (OIDC) authentication, allowing user
    GOOGLE_CLIENT_SECRET=your-client-secret
    ```
 
-3. **Run the database migration**:
-   ```bash
-   python app/migrations/001_add_oidc_fields.py
-   ```
-
-4. **Restart your application**:
+3. **Restart your application**:
    ```bash
    # If using Docker
    docker-compose restart