docs: add github environment setup steps

DEPLOYMENT.md

@@ -202,6 +202,25 @@ In GitHub:
    - `development`
    - `production`
 
+### Exact GitHub UI path
+1. Open the private repository:
+   - `https://github.com/Bostame/workdock-platform`
+2. Click:
+   - `Settings`
+3. In the left sidebar, open:
+   - `Environments`
+4. Click:
+   - `New environment`
+5. Create:
+   - `development`
+6. Repeat and create:
+   - `production`
+7. Open the `development` environment
+8. Under `Environment secrets`, click:
+   - `Add environment secret`
+9. Add each required secret one by one
+10. Repeat the same pattern later for `production`
+
 ### Development environment secrets
 Add:
 - `TEST_DEPLOY_HOST`
@@ -217,6 +236,49 @@ Current test values:
 - `TEST_DEPLOY_PATH=/opt/workdock`
 - `TEST_DEPLOY_SSH_KEY=<private key that can ssh to root@192.168.2.55>`
 
+### Development secret entry example
+Use these exact values in the `development` environment:
+
+`TEST_DEPLOY_HOST`
+```text
+192.168.2.55
+```
+
+`TEST_DEPLOY_USER`
+```text
+root
+```
+
+`TEST_DEPLOY_PORT`
+```text
+22
+```
+
+`TEST_DEPLOY_PATH`
+```text
+/opt/workdock
+```
+
+`TEST_DEPLOY_SSH_KEY`
+```text
+<paste the full private SSH key that can log in to root@192.168.2.55>
+```
+
+The SSH key must include the full multi-line content, for example:
+```text
+-----BEGIN OPENSSH PRIVATE KEY-----
+...
+-----END OPENSSH PRIVATE KEY-----
+```
+
+### How to verify the SSH key before adding it
+From your local machine:
+```bash
+ssh -4 root@192.168.2.55
+```
+
+If that works without asking for a password, the matching private key is the correct one to store in `TEST_DEPLOY_SSH_KEY`.
+
 ### Production environment secrets
 Add:
 - `PROD_DEPLOY_HOST`
@@ -239,6 +301,38 @@ From GitHub Actions:
 1. open `Deploy Test`
 2. click `Run workflow`
 
+### First GitHub Actions validation
+After you add the `development` environment secrets:
+1. Open:
+   - `https://github.com/Bostame/workdock-platform/actions`
+2. Open workflow:
+   - `Deploy Test`
+3. Click:
+   - `Run workflow`
+4. Select branch:
+   - `develop`
+5. Run it
+6. Wait until both steps complete:
+   - upload bundle
+   - deploy over SSH
+7. Verify:
+   - `http://192.168.2.55:8088/healthz/`
+8. Then open the app home page in the browser
+
+### What success looks like
+- workflow status is green in GitHub Actions
+- `Deploy Test` job finishes without SSH or health-check errors
+- `/healthz/` returns `200 OK`
+- the containers on the test server remain up
+
+### If the workflow fails
+Check in this order:
+1. wrong or incomplete `TEST_DEPLOY_SSH_KEY`
+2. wrong `TEST_DEPLOY_USER`
+3. wrong `TEST_DEPLOY_PATH`
+4. changed server host key
+5. server disk-space or Docker runtime issue
+
 ## How to validate a deployment
 ### From your machine
 ```bash