style: stack per-class override rows instead of a wide table (REQ-181 layout)

The width:100% table plus the new MaxBox column let the Class column absorb
the slack, stranding the Container checkbox away from its class. One block
per class now: name + Container checkbox on the first line, Conf/IoU/MinBox/
MaxBox inputs in a wrapping grid below. Behavior identical - KEYS,
buildClassParams, compose() copy line, toggleContainer revert, aria labels.

docs/ui-spec.md

@@ -449,9 +449,13 @@ Two columns inside one dialog (920 px wide, max 96 vw / 90 vh, scrollable).
 - Confidence threshold — 0.05…0.95 step 0.05, default 0.35.
 - NMS IoU threshold — 0…0.9 step 0.05, default 0.0.
 - Min box size (fraction of frame) — 0…0.5 step 0.005, default 0, shown as a percentage.
-- **Per-class overrides** (REQ-181) — a compact table below the sliders, one row per currently
-  selected class: `Conf` / `IoU` / `MinBox` / `MaxBox` number inputs and a **Container** checkbox
-  (REQ-184). Each input's placeholder shows the current global value and an empty input
+- **Per-class overrides** (REQ-181) — one **stacked block** per currently selected class
+  below the sliders: the class name on the first line with its **Container** checkbox
+  (REQ-184) at the right, then a wrapping grid of `Conf` / `IoU` / `MinBox` / `MaxBox`
+  number inputs, each labelled in its own colour. No column headers, no wide table — a
+  narrow modal wraps the grid instead of squeezing the numbers, and the checkbox never
+  drifts away from its class. Each input's placeholder shows the current global value and
+  an empty input
   inherits it; only filled cells are sent, as
   `class_params` on **both** the preview and the job request, so preview and run cannot
   disagree. Classes without an override behave exactly as before. The checkbox marks the
@@ -462,7 +466,7 @@ Two columns inside one dialog (920 px wide, max 96 vw / 90 vh, scrollable).
   unmarked classes are governed by IoU alone. Toggling is optimistic
   `PATCH /projects/{id} { containers: { [classId]: bool } }` into `project_classes.container`
   with revert on rejection — preview and batch job read the same stored flag.
-- **Copy (REQ-186)** — small right-aligned ghost button above the overrides table; label
+- **Copy (REQ-186)** — small right-aligned ghost button above the overrides block; label
   `Copy`, flips to `Copied` for 1.5 s inside an `aria-live` span, and on failure silently
   stays `Copy`. One line per selected class, e.g.
   `class sack conf 0.4 iou 0.6 minbox 0.005 maxbox 1 container false` — an empty input copies the
@@ -537,8 +541,8 @@ Same anatomy, wider (1040 px), with three differences:
   must not abort the rest; the backend GPU lock serialises the real work anyway. Progress is
   reported as `done/total (failed)` and the result message is `Queued N auto-annotation job(s)`.
 
-The per-class overrides table (REQ-181) appears here too, below the sliders — same columns
-including the **Container** checkbox (REQ-184) — and its
+The per-class overrides block (REQ-181) appears here too, below the sliders — the same
+stacked rows, **Container** checkbox (REQ-184) included — and its
 `class_params` ride along on every preview and start request — one set of overrides applies
 to all selected batches.