implemented 02-git-gateway.md: added Git access layer with credentials bridge, duration parser, and extensive tests

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

@@ -0,0 +1,19 @@
+package de.hoennig.gittally.config
+
+import java.time.Duration
+
+/** Parses durations in the `watcher.newBranchMaxAge` format: `5d` (days) or `12h` (hours). */
+object DurationParser {
+    private val pattern = Regex("""(\d+)([dh])""")
+
+    fun parse(value: String): Duration {
+        val match =
+            pattern.matchEntire(value.trim())
+                ?: throw IllegalArgumentException("invalid duration '$value': expected <amount>d or <amount>h, e.g. 5d or 12h")
+        val (amount, unit) = match.destructured
+        return when (unit) {
+            "d" -> Duration.ofDays(amount.toLong())
+            else -> Duration.ofHours(amount.toLong())
+        }
+    }
+}