add GitHub Actions workflow for Bash syntax checking and enhance README with usage examples

.gitea/workflows/syntax-check.yml

@@ -0,0 +1,43 @@
+name: Bash Syntax Check
+
+on:
+  push:
+    branches:
+      - main
+      - master
+      - develop
+    paths:
+      - 'slackecho'
+      - '.gitea/workflows/syntax-check.yml'
+  pull_request:
+    branches:
+      - main
+      - master
+      - develop
+    paths:
+      - 'slackecho'
+
+jobs:
+  syntax-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Install shellcheck
+        run: sudo apt-get update && sudo apt-get install -y shellcheck
+
+      - name: Run bash syntax check
+        run: bash -n slackecho
+
+      - name: Run shellcheck analysis
+        run: shellcheck slackecho
+
+      - name: Verify script is executable
+        run: |
+          if [[ -x slackecho ]]; then
+            echo "✓ slackecho has executable permission"
+          else
+            echo "✗ slackecho is missing executable permission"
+            exit 1
+          fi