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",