feat(v5-g19): DimensionsTab Apply per-row button + callback

Closes V5-G19 / cppmega-mlx-udk. DimensionsTab rows for auto-inferred
params get an Apply button (data-testid=dim-row-{brick}-{param}-apply).
onApply(entry) callback fires; parent dispatches spec mutation so the
next verify hides the now-fulfilled suggestion (feedback loop closed).

3 new vitest. UI wiring to App.tsx dispatch deferred — backend
contract + component contract first, App integration follow-up.

Author: apstenku123

vbgui/src/components/sidebar/DimensionsTab.tsx

@@ -15,10 +15,14 @@ export interface InferenceEntryClient {
 export interface DimensionsTabProps {
   log: InferenceEntryClient[];
   onHighlight?: (brick: string) => void;
+  /** G19: callback when user clicks Apply on an auto-inferred row.
+   *  Parent dispatches the spec mutation so subsequent verify hides
+   *  the suggestion (closing the loop). */
+  onApply?: (entry: InferenceEntryClient) => void;
 }
 
 export function DimensionsTab({
-  log, onHighlight,
+  log, onHighlight, onApply,
 }: DimensionsTabProps): JSX.Element {
   const [filterSource, setFilterSource] =
     useState<"all" | "user" | "auto">("all");
@@ -70,6 +74,7 @@ export function DimensionsTab({
             <th style={th}>Value</th>
             <th style={th}>Source</th>
             <th style={th}>Reason</th>
+            <th style={th}></th>
           </tr>
         </thead>
         <tbody>
@@ -96,6 +101,16 @@ export function DimensionsTab({
               <td style={{ ...td, color: "#6b7280", fontSize: 11 }}>
                 {e.reason}
               </td>
+              <td style={td}>
+                {onApply && e.source === "auto" && (
+                  <button data-testid={`dim-row-${e.brick}-${e.param}-apply`}
+                          onClick={(ev) => { ev.stopPropagation();
+                                             onApply(e); }}
+                          style={{ fontSize: 10, padding: "1px 6px" }}>
+                    Apply
+                  </button>
+                )}
+              </td>
             </tr>
           ))}
           {visible.length === 0 && (

vbgui/tests/DimensionsTab.test.tsx

@@ -57,4 +57,36 @@ describe("DimensionsTab", () => {
     render(<DimensionsTab log={[]} />);
     expect(screen.getByText(/No matching entries/)).toBeTruthy();
   });
+
+  // G19: Apply button on auto rows
+  it("G19: Apply button visible only on auto-source rows", () => {
+    const log = [
+      { brick: "attn", param: "head_dim", value: 64,
+        source: "auto" as const, reason: "inferred from H" },
+      { brick: "mlp", param: "intermediate_size", value: 256,
+        source: "user" as const, reason: "user set" },
+    ];
+    render(<DimensionsTab log={log} onApply={() => {}} />);
+    expect(screen.getByTestId("dim-row-attn-head_dim-apply")).toBeTruthy();
+    expect(screen.queryByTestId(
+      "dim-row-mlp-intermediate_size-apply")).toBeNull();
+  });
+
+  it("G19: clicking Apply fires onApply(entry)", () => {
+    const onApply = vi.fn();
+    const entry = { brick: "attn", param: "head_dim", value: 64,
+                    source: "auto" as const, reason: "inferred from H" };
+    render(<DimensionsTab log={[entry]} onApply={onApply} />);
+    fireEvent.click(screen.getByTestId("dim-row-attn-head_dim-apply"));
+    expect(onApply).toHaveBeenCalledWith(entry);
+  });
+
+  it("G19: Apply button absent when onApply prop missing", () => {
+    render(<DimensionsTab log={[
+      { brick: "attn", param: "head_dim", value: 64,
+        source: "auto", reason: "x" },
+    ]} />);
+    expect(screen.queryByTestId(
+      "dim-row-attn-head_dim-apply")).toBeNull();
+  });
 });