feat(frontend): English UI + 'Datamart Builder with Human In The Loop' tagline

The interface is now fully English regardless of the chat language (session
titles stay in whatever language the user typed). Changed the right-rail
subtitle to 'Datamart Builder with Human In The Loop'. Translated all chrome:
new-question/settings dialogs, workflow phase strip (F1-F8), session rail,
steer input, widgets (select/multiselect/freetext/fallback/reserved controls)
and viewers (SQL, results, schema linking). Test matchers updated in lockstep.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/viewers/SchemaLinkingViewer.tsx

@@ -109,19 +109,19 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
           disabled={oversized}
           className={view === "chart" ? "font-bold" : ""}
         >
-          Grafico
+          Graph
         </button>
         <button
           onClick={() => setView("table")}
           className={view === "table" ? "font-bold" : ""}
         >
-          Tabella
+          Table
         </button>
       </div>
 
       {oversized && (
         <p className="text-sm text-amber-600">
-          Troppi elementi per il grafico, usa la tabella
+          Too many elements for the graph, use the table
         </p>
       )}
 
@@ -137,9 +137,9 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
         <table className="w-full text-sm border-collapse">
           <thead>
             <tr>
-              <th className="text-left border-b py-1">Nome</th>
-              <th className="text-left border-b py-1">Tipo</th>
-              <th className="text-left border-b py-1">Perché</th>
+              <th className="text-left border-b py-1">Name</th>
+              <th className="text-left border-b py-1">Type</th>
+              <th className="text-left border-b py-1">Why</th>
             </tr>
           </thead>
           <tbody>
@@ -147,7 +147,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
               <React.Fragment key={table.name}>
                 <tr className="font-semibold bg-muted/30">
                   <td className="py-1 pl-1">{table.name}</td>
-                  <td>tabella</td>
+                  <td>table</td>
                   <td className="text-xs text-muted-foreground">
                     {reasonFor(table)}
                   </td>
@@ -157,7 +157,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
                     <td className="py-0.5 pl-4 text-muted-foreground">
                       {col.name}
                     </td>
-                    <td>colonna</td>
+                    <td>column</td>
                     <td className="text-xs text-muted-foreground">
                       {reasonFor(col)}
                     </td>
@@ -170,7 +170,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
                 <td className="py-0.5 pl-1 text-muted-foreground">
                   {col.name}
                 </td>
-                <td>colonna</td>
+                <td>column</td>
                 <td className="text-xs text-muted-foreground">
                   {reasonFor(col)}
                 </td>