fix(coach): dock the conversations panel flush against the right edge

The Coach page cancelled the shell's container padding with negative
margins, so <main> kept its reserved scrollbar gutter and painted a dead
strip to the right of the panel on classic-scrollbar platforms. The shell
now renders /coach full bleed: no centred container, no padding and no
reserved gutter, and the page fills what <main> leaves below the top bar.
A refusal card (shared record, module off) keeps the padded frame.

The panel header takes one 12 px inset with a gap of 8 between title and
icons, a text-lg title, and 28 px icon buttons beside a pointer (44 px on
touch). Conversation rows take the control radius and a 36 px pointer
floor.

src/app/coach/page-client.tsx

@@ -263,22 +263,12 @@ export default function CoachPageClient() {
     <div
       data-slot="coach-page"
       data-tour-id="coach-hero"
-      // v1.18.10 (W4) — full-bleed conversation surface. Cancel the
-      // AuthShell container's padding (`-mt-6` top, `-mb-20` bottom,
-      // `-mx-4 md:-mx-6` sides) so the chat is edge-to-edge and claims the
-      // full viewport height minus the top bar (`4rem`). No inner card:
-      // `<CoachConversation>` paints directly onto the page so it reads as
-      // one continuous conversation, not a window inside a window. The
-      // separate bottom-right FAB/overlay drawer stays the compact surface.
-      //
-      // v1.18.10 (W10) — height is mobile-aware. The fixed `<BottomNav>`
-      // (64px + iOS home-indicator inset) is mobile-only; the desktop
-      // full-bleed layout has no bottom nav. On mobile the page must subtract
-      // the TopBar (`4rem`) AND the BottomNav band (`4rem` +
-      // `env(safe-area-inset-bottom)`) so the docked composer / Stop control
-      // always clears the nav instead of sitting under it. On `md+` the nav
-      // is hidden, so the page reclaims the full height below the TopBar.
-      className="bg-background -mx-4 -mt-6 -mb-20 flex h-[calc(100dvh-8rem-env(safe-area-inset-top,0px)-env(safe-area-inset-bottom,0px))] min-h-[32rem] flex-col overflow-hidden md:-mx-6 md:h-[calc(100dvh-4rem)]"
+      // Full-bleed conversation surface. The shell renders `/coach` without
+      // its centred container, padding or reserved scrollbar gutter, and its
+      // `<main>` already clears the top bar and, on phones, the bottom nav,
+      // so the page simply fills what is left. No inner card: the
+      // conversation paints directly onto the page.
+      className="bg-background flex min-h-[32rem] flex-1 flex-col overflow-hidden"
     >
       {/* `useSearchParams` requires a Suspense boundary so the client-search
           bailout never opts the whole route out of static optimisation. */}