fix(persist): one shared z-order across Source + WebcamSceneConfig rows

A webcam dragged between sources reverted to the bottom of the stack on
every relaunch: Source and WebcamSceneConfig each carried independent
per-type SortOrder counters, and Load appended all Sources before all
configs. Save now stamps both tables' SortOrder from the element's index
within scene.Elements; Load merges the two tables' rows by that shared z
(sources-first tie-break preserves legacy rows). Cross-type reorder now
survives a fresh LayoutStore reload.

Task 37 queued: defaults vs current layout split (creator directive) —
capture out-of-scope work in TASKS.md rather than folding it in.

TASKS.md

@@ -52,6 +52,7 @@
 | 34 | Scheduled streams (Text-drawer version) | ☐ Queued (2026-09-01) | [`TASKS/task-34-scheduled-streams.md`](TASKS/task-34-scheduled-streams.md) |
 | 35 | Scene-linked audio | ☐ Queued (2026-09-01) | [`TASKS/task-35-scene-linked-audio.md`](TASKS/task-35-scene-linked-audio.md) |
 | 36 | Gold pass | ☐ Queued (2026-09-01) | [`TASKS/task-36-gold-pass.md`](TASKS/task-36-gold-pass.md) |
+| 37 | Defaults vs current layout split | ☐ Queued (2026-09-20) | [`TASKS/task-37-defaults-current-split.md`](TASKS/task-37-defaults-current-split.md) |
 
 ---
 
@@ -73,6 +74,10 @@
   adopts a solo camera as default. TASK 26's app-wide gate superseded by creator directive. Next
   slices (user-queued): multi-camera webcam selector in the App Settings dialog (gear), static (+)
   catalog rows (Background, YouTubeEvent, quoted labels) with reason-greying.
+- **TASK 37** — queued (2026-09-20): split the layout data into a `default` set (the established DB)
+  and a `current` set carrying the build-id; a saved `current` is honored only by the same build-id,
+  otherwise defaults load — enables one-click revert to defaults too. Capture needed work OUT of
+  current scope here; do not bolt it onto an in-flight change.
 
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