fix(coach): centre the composer text in its input pill

On a phone the placeholder sat noticeably low. The composer row was
bottom-aligned so the send button would stay beside the last line as the
textarea grows, but that also bottom-aligned a single-line textarea against
a 44 px touch target: 7 px of space above the text and 1 px below.

The row centres its textarea now and the controls keep their own bottom
alignment, so both properties hold. Measured empty, one line and four
lines, phone and desktop: the single-line gap goes 7/1 to 4/4 on a phone
and 2/1 to 2/2 on desktop, and the multi-line case is unchanged with the
send button still level with the last line.

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

@@ -267,11 +267,15 @@ describe("<CoachInput>", () => {
     expect(controls?.[0]).not.toMatch(/\bjustify-between\b/);
     expect(controls?.[0]).toMatch(/\bshrink-0\b/);
 
-    // And the row itself is a row at every width, bottom-aligned so the send
-    // button stays beside the last line as the textarea grows.
+    // And the row itself is a row at every width. The textarea is centred in
+    // it — bottom-aligning a one-line textarea against a 44 px tap target left
+    // the placeholder sitting visibly low in the pill — while the controls
+    // keep their own bottom alignment, so the send button stays beside the
+    // LAST line as the textarea grows rather than drifting to the middle.
     const shell = html.match(/<div[^>]*class="[^"]*\bflex-row\b[^"]*"[^>]*>/);
-    expect(shell?.[0]).toMatch(/\bitems-end\b/);
+    expect(shell?.[0]).toMatch(/\bitems-center\b/);
     expect(shell?.[0]).not.toMatch(/\bflex-col\b/);
+    expect(controls?.[0]).toMatch(/\bself-end\b/);
   });
 
   it("sizes the hub actions trigger to the 44px tap-target floor on phones", () => {

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

@@ -427,9 +427,15 @@ export function CoachInput({
           // hold: focus follows DOM order, and the DOM order (textarea,
           // actions, Send) is identical in both layouts. Nothing jumps.
           //
-          // `items-end` keeps the controls beside the LAST line as the textarea
-          // grows, so the send button stays where the thumb left it.
-          "flex flex-row items-end gap-1.5 p-1.5",
+          // `items-center` with the controls pinned `self-end` below. The row
+          // used to be `items-end` throughout, which bottom-aligned an empty
+          // one-line textarea against a 44 px touch target: the placeholder sat
+          // roughly 6 px low in the pill, reading as if the text had slipped.
+          // Centring the textarea fixes the empty and single-line cases, and
+          // `self-end` on the controls preserves the reason `items-end` was
+          // there — as the textarea grows, the send button stays beside the
+          // LAST line rather than drifting to the middle.
+          "flex flex-row items-center gap-1.5 p-1.5",
         )}
       >
         <textarea
@@ -455,7 +461,7 @@ export function CoachInput({
         />
         <div
           data-slot="coach-input-controls"
-          className="order-2 flex shrink-0 items-center gap-1.5"
+          className="order-2 flex shrink-0 items-center gap-1.5 self-end"
         >
           <div
             data-slot="coach-input-leading"