Build definitions with onPush/atTimes replace branch-owned schedules

ADR 0007: the YAML builds section (next to the reserved maxConcurrent
key) defines named builds (jobs) with onPush/atTimes triggers, branch
selectors (name globs, activeWithin age filter), and build-setting
overrides applied last over the merged branch config. The implicit
default build (onPush over all branches) preserves the previous
behavior; the section is pinned against the worktree layer.

Results record the job name; restart, retry, and startup recovery
re-run by it, resolving settings from the current config. A non-default
build records under the <branch>@<build> pool with its own row,
retention count, and permanent latest-green link.

branches.*.autoBuild stays as a deprecated alias (plain times only);
the unreleased-in-practice v0.9.13 per-slot buildCommand/name syntax is
removed again.

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

src/main/kotlin/de/hoennig/gittally/git/GitService.kt

@@ -140,6 +140,19 @@ class GitService(
             }.map { (branch, _) -> branch }
     }
 
+    /** Committer timestamps of all origin branch heads, in one git call; used by `activeWithin` build selectors. */
+    fun originBranchCommitTimes(workingDir: Path = Paths.get(".")): Map<String, Instant> =
+        runner
+            .runOrThrow(
+                listOf("git", "for-each-ref", "--format=%(refname:strip=3) %(committerdate:unix)", "refs/remotes/origin"),
+                workingDir,
+            ).lines()
+            .mapNotNull { line ->
+                val branch = line.substringBeforeLast(' ')
+                val epochSeconds = line.substringAfterLast(' ').toLongOrNull() ?: return@mapNotNull null
+                if (branch == "HEAD") null else branch to Instant.ofEpochSecond(epochSeconds)
+            }.toMap()
+
     /** Switches to an existing local branch, or creates a tracking branch from origin. */
     fun checkout(
         branch: String,