move terminal-verbosity toggle from agent overflow menu to /settings.html

Per mara: 'i wanted you to put this in .../settings.html' — the toggle
belongs with the other operator-local browser preferences, not buried
in each agent's own overflow menu.

Extracted the get/set + localStorage key into @hive/shared/prefs.js so
settings.html (writer) and every per-agent app.js (reader, via
HiveTerminal.create's expandDetails option) agree on the exact same key
without two independently-typed copies that could drift. Removed the
now-unused overflow-menu toggle + its agent.css rules from the agent
page. Docs moved from docs/web-ui/agent.md's overflow-button section to
docs/web-ui/dashboard.md's S3TT1NGS section, next to the existing
browser-notifications preference.

frontend/packages/shared/package.json

@@ -17,6 +17,7 @@
     "./terminal.css": "./src/terminal/terminal.css",
     "./chrome.css": "./src/chrome.css",
     "./forms.js": "./src/forms.js",
+    "./prefs.js": "./src/prefs.js",
     "./dom.js": "./src/dom.js",
     "./modal.js": "./src/modal.js",
     "./shadow-css.js": "./src/shadow-css.js",

frontend/packages/shared/src/prefs.js

@@ -0,0 +1,27 @@
+// 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 on /settings.html applies to the next
+// rendered row in any already-open agent tab without a reload.
+export function getExpandDetailsPref() {
+  try { return localStorage.getItem(EXPAND_DETAILS_KEY) === '1'; }
+  catch { return false; }
+}
+export function setExpandDetailsPref(v) {
+  try {
+    if (v) localStorage.setItem(EXPAND_DETAILS_KEY, '1');
+    else localStorage.removeItem(EXPAND_DETAILS_KEY);
+  } catch { /* localStorage unavailable — preference is session-only */ }
+}