Let auto-build slots run their own build command under their own name

A branches.<name>.autoBuild.times entry is now either a plain HH:MM
string or an object with time, its own buildCommand, and a name, so a
nightly slot can run a fuller check than the on-commit builds. The
watcher passes the slot's command and name to the executor, persisted in
the build result — UI restarts, gittally retry, and the startup recovery
repeat a build with the command and name it originally ran under.

A named slot (e.g. master@nightly) gets its own pool: repository
grouping, retention count, branches-view row (sorted after its branch),
latest status, and permanent latest-green artifact link are keyed by the
build name, while origin lookups, gone-branch pruning, worktrees, and
Gitea links/statuses stay keyed by the real branch. Without a name,
slot builds share the branch's pool as before.

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

src/main/kotlin/de/hoennig/gittally/config/GitTallyConfig.kt

@@ -1,5 +1,8 @@
 package de.hoennig.gittally.config
 
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
+
 data class GitTallyConfig(
     val server: ServerConfig = ServerConfig(),
     val git: GitConfig = GitConfig(),
@@ -148,5 +151,30 @@ data class DockerConfig(
 
 data class AutoBuildConfig(
     val enabled: Boolean = false,
-    val times: List<String> = listOf("01:00"),
+    /**
+     * Daily UTC slots. Each entry is either a plain `HH:MM` time or an object with
+     * `time` and its own `buildCommand` — so a nightly slot can run a fuller check
+     * than the on-commit builds of the same branch.
+     */
+    val times: List<AutoBuildSlot> = listOf(AutoBuildSlot("01:00")),
+)
+
+/**
+ * One scheduled auto-build slot; in YAML either a plain `HH:MM` string or an object
+ * (`time` plus optional `buildCommand` and `name`) — see [AutoBuildSlotDeserializer].
+ */
+@JsonDeserialize(using = AutoBuildSlotDeserializer::class)
+@JsonSerialize(using = AutoBuildSlotSerializer::class)
+data class AutoBuildSlot(
+    /** UTC time of day, `HH:MM`. */
+    val time: String,
+    /** Command this slot's build runs; empty runs the branch's [BranchConfig.buildCommand]. */
+    val buildCommand: String = "",
+    /**
+     * Build name this slot's builds are recorded under (e.g. `master@nightly`); empty
+     * records them under the branch name. A named slot gets its own history, retention
+     * pool, latest status, and permanent latest-green artifact link, so its builds are
+     * not displaced by the branch's regular builds.
+     */
+    val name: String = "",
 )