fix(ci): Escape dollar signs for shell variables in Woodpecker

Woodpecker interprets $ as variable substitution in YAML, so we need to
use $$ to escape it and pass a literal $ to the shell script.

Changed from a for loop to explicit function calls with escaped variables:
- Use $$ instead of $ for all shell variables
- Function-based approach for cleaner variable passing
- Each package explicitly called: link_package "stack-api" etc.

This fixes the variable expansion issue where ${package} was empty,
resulting in URLs like "container//-/link/stack" (double slash).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.woodpecker.yml

@@ -278,18 +278,24 @@ steps:
     commands:
       - apk add --no-cache curl
       - |
-        for package in stack-api stack-web stack-postgres stack-openbao stack-orchestrator; do
-          STATUS=$(curl -s -o /dev/null -w "%{http_code}" -X POST \
-            -H "Authorization: token $GITEA_TOKEN" \
-            "https://git.mosaicstack.dev/api/v1/packages/mosaic/container/${package}/-/link/stack")
-          if [ "$STATUS" = "201" ] || [ "$STATUS" = "204" ]; then
-            echo "✅ Linked ${package} to stack"
-          elif [ "$STATUS" = "400" ]; then
-            echo "✅ ${package} already linked (OK)"
+        link_package() {
+          PKG="$$1"
+          STATUS=$$(curl -s -o /dev/null -w "%{http_code}" -X POST \
+            -H "Authorization: token $$GITEA_TOKEN" \
+            "https://git.mosaicstack.dev/api/v1/packages/mosaic/container/$$PKG/-/link/stack")
+          if [ "$$STATUS" = "201" ] || [ "$$STATUS" = "204" ]; then
+            echo "✅ Linked $$PKG to stack"
+          elif [ "$$STATUS" = "400" ]; then
+            echo "✅ $$PKG already linked (OK)"
           else
-            echo "❌ Warning: ${package} link returned $STATUS"
+            echo "❌ $$PKG link failed with status $$STATUS"
           fi
-        done
+        }
+        link_package "stack-api"
+        link_package "stack-web"
+        link_package "stack-postgres"
+        link_package "stack-openbao"
+        link_package "stack-orchestrator"
     when:
       - branch: [main, develop]
         event: [push, manual, tag]