added age-based build retention: artifacts.retentionMaxAge (e.g. 30d, empty = no limit) drops builds older than the given age; combines with retentionPerBranch as independent caps — a build is kept only while it satisfies both limits; a branch's newest build is never age-pruned and keepLatestGreen now shields the latest green build from both limits, keeping the permanent /branches/... links valid

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/test/kotlin/de/hoennig/gittally/watcher/WatcherTest.kt

@@ -420,6 +420,18 @@ class WatcherTest : FunSpec() {
             dropping.repository.history().map { it.status } shouldContainExactly listOf(BuildStatus.FAILED)
         }
 
+        test("poll drops builds older than retentionMaxAge but keeps the branch's newest build") {
+            // seeds start one hour before the fixed clock, so a 30m age limit cuts them off
+            val harness = Harness(GitTallyConfig(artifacts = ArtifactsConfig(retentionMaxAge = "30m")))
+            harness.seed("main", BuildStatus.FAILED, commit = "commit-1")
+            harness.seed("main", BuildStatus.FAILED, commit = "commit-2")
+            every { harness.gitService.originBranches(any()) } returns listOf("main")
+
+            harness.watcher.poll(harness.workingDir)
+
+            harness.repository.history().map { it.commit } shouldContainExactly listOf("commit-2")
+        }
+
         test("worktrees of queued or running builds are never pruned") {
             val harness = Harness()
             harness.seed("busy", BuildStatus.RUNNING, commit = "commit-1")