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/shared/src/prefs.ts

@@ -0,0 +1,32 @@
+// Tiny browser-local (localStorage) preference helpers shared by the
+// dashboard's /settings.html and the per-agent page — both need the
+// exact same key name to actually talk to each other via the browser's
+// shared per-origin storage (settings.html is where the operator sets
+// the preference; every per-agent page's terminal reads it), so the
+// get/set pair — and the key itself — live here once rather than as
+// independent copies in each package that could drift out of sync.
+
+const EXPAND_DETAILS_KEY = 'hive-agent-expand-details';
+
+// Whether a per-agent terminal's otherwise-collapsed `<details>` panels
+// (long tool-results, Write/Edit diffs, …) should default open. Pure
+// client-side — no backend field, nothing round-trips through
+// `/api/*`. Read live (not cached) by the shared terminal factory's
+// `expandDetails` option — see docs/web-ui/shape.md::Shared terminal
+// pane — so a preference change applies to the next rendered row in
+// any already-open agent tab without a reload.
+export function getExpandDetailsPref(): boolean {
+  try {
+    return localStorage.getItem(EXPAND_DETAILS_KEY) === '1';
+  } catch {
+    return false;
+  }
+}
+export function setExpandDetailsPref(v: boolean): void {
+  try {
+    if (v) localStorage.setItem(EXPAND_DETAILS_KEY, '1');
+    else localStorage.removeItem(EXPAND_DETAILS_KEY);
+  } catch {
+    /* localStorage unavailable — preference is session-only */
+  }
+}