agent term: move expand-tool-output setting into its own settings popup

mara, #3778: the toggle lived on the separate hive-dashboard's
/settings.html even though it's agent-terminal-only. Moved it into
SettingsMenu (shared with swarm-ui) behind an opt-in showExpandDetails
prop — only the agent page passes it, matching her caution that the
component is shared but this setting isn't.

Also found and fixed a real regression while touching this: the
Preact rewrite's classifyEvent.ts hardcodes defaultOpen: true only for
the always-open markdown-bearing rows (send/ask/answer/recv) and never
reads the preference at all for the rows it's actually meant to
control (diffs, plain tool output, long errors) — so the toggle
currently has zero effect on the live page. Wired
getExpandDetailsPref() into those four sites; the always-open rows are
untouched, matching the documented pre-rewrite behavior.

Converted prefs.js to prefs.ts (TS couldn't resolve types for a plain
.js import) — same public @hive/shared/prefs.js export path, matching
how badge.js/icons.js etc. already map a .js export name to a
.tsx/.ts source file.

frontend/packages/agent/src/Root.tsx

@@ -113,7 +113,7 @@ export function Root() {
           dashboardBase={resolveDashboardBase(state.dashboard_port)}
         />
       ) : null}
-      <SettingsMenu themeKey={THEME_KEY} motionKey={MOTION_KEY} />
+      <SettingsMenu themeKey={THEME_KEY} motionKey={MOTION_KEY} showExpandDetails />
     </>
   );
   // Kept mounted regardless of `openPanel` (open/closed toggles just the