refactor(web): unify message-direction arrows and rename Pinned section (#1623)

- Direction labels now both point right so the arrow reads clearly at
  badge size: incoming "client ← server" becomes "server → client"
  (from → to), in MessageDirectionBadge and MessageDirectionFilter
  (shared by the Protocol and Network views).
- The Protocol list's pinned section header now reads "Pinned Messages"
  (was "Pinned Requests"), matching the "Messages" panel title.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw

clients/web/src/components/groups/ProtocolEntry/ProtocolEntry.test.tsx

@@ -158,11 +158,11 @@ describe("ProtocolEntry", () => {
     expect(screen.getByText("client → server")).toBeInTheDocument();
   });
 
-  it("shows client ← server for a server-originated entry", () => {
+  it("shows server → client for a server-originated entry", () => {
     renderWithMantine(
       <ProtocolEntry {...baseProps} entry={notificationEntry} />,
     );
-    expect(screen.getByText("client ← server")).toBeInTheDocument();
+    expect(screen.getByText("server → client")).toBeInTheDocument();
   });
 
   it("renders Pin label when not pinned", () => {