fix(coach): keep the composer placeholder on one line

Shorten the composer placeholder across all locales to a short, inviting
one-liner and clip the placeholder pseudo-element so a longer hint can
never wrap to a second line inside the single-row composer on a narrow
phone. The textarea value still wraps and auto-grows for real typing.

src/components/insights/coach-panel/__tests__/coach-input.test.tsx

@@ -49,7 +49,7 @@ describe("<CoachInput>", () => {
     const html = render(
       <CoachInput value="" onChange={() => {}} onSubmit={() => {}} />,
     );
-    expect(html).toContain("Ask anything about your data");
+    expect(html).toContain("Ask me anything");
     expect(html).not.toContain('data-slot="coach-input-hint"');
     expect(html).not.toContain("Press Enter to send");
     expect(html).toContain('data-slot="coach-input-send"');
@@ -60,7 +60,7 @@ describe("<CoachInput>", () => {
       <CoachInput value="" onChange={() => {}} onSubmit={() => {}} />,
       "de",
     );
-    expect(html).toContain("Frag mich etwas zu deinen Daten");
+    expect(html).toContain("Frag mich etwas");
   });
 
   it("disables the send button when the value is empty", () => {

src/components/insights/coach-panel/coach-input.tsx

@@ -567,6 +567,11 @@ export function CoachInput({
             // scroll regions). Scoped here, not in globals.css.
             "[scrollbar-width:thin] [scrollbar-color:color-mix(in_srgb,var(--dracula-purple)_35%,transparent)_transparent]",
             "placeholder:text-muted-foreground disabled:opacity-60",
+            // Keep the placeholder a single line on narrow phones: a long
+            // hint used to wrap to two lines inside the one-row composer and
+            // read as a cramped block. Clip the PLACEHOLDER pseudo only — the
+            // textarea value still wraps and auto-grows for real typing.
+            "placeholder:overflow-hidden placeholder:text-ellipsis placeholder:whitespace-nowrap",
           )}
         />
         {showHub ? (