feat: add BranchStrategy class

Mirrors company BasePipeline pattern. Static methods determine
what pipeline stages run per branch:
- PR-*: test only
- feature/*: test + build/push + helm bump + git push
- develop/main/release/hotfix: test + build/push only

imageTag() returns branch-appropriate tag format:
release/x.y.z -> x.y.z, others -> <prefix>-<random8>

src/vn/fireflylab/pipeline/BranchStrategy.groovy

@@ -0,0 +1,31 @@
+package vn.fireflylab.pipeline
+
+class BranchStrategy implements Serializable {
+
+    static boolean isPR(String branch)      { branch ==~ /^PR-\d+$/ }
+    static boolean isFeature(String branch) { branch ==~ /^feature\/.+/ }
+    static boolean isDevelop(String branch) { branch == 'develop' }
+    static boolean isMain(String branch)    { branch == 'main' }
+    static boolean isRelease(String branch) { branch ==~ /^release\/\d+\.\d+\.\d+$/ }
+    static boolean isHotfix(String branch)  { branch ==~ /^hotfix\/.+/ }
+
+    // Build + push on all branches except PRs
+    static boolean shouldBuildImage(String branch) {
+        return !isPR(branch)
+    }
+
+    // Helm bump + git commit/push only on feature branches
+    static boolean shouldBumpChart(String branch) {
+        return isFeature(branch)
+    }
+
+    static String imageTag(String branch) {
+        if (isRelease(branch)) return branch.replaceFirst('release/', '')
+        def shortId = UUID.randomUUID().toString().take(8)
+        if (isMain(branch))    return "main-${shortId}"
+        if (isDevelop(branch)) return "dev-${shortId}"
+        if (isHotfix(branch))  return "hotfix-${shortId}"
+        // feature/* and anything else: sanitize branch name + random suffix
+        return "${branch.replaceAll('[^a-zA-Z0-9._-]', '-')}-${shortId}"
+    }
+}