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/package.json

@@ -21,7 +21,7 @@
     "./chrome.css": "./src/chrome.css",
     "./pill.css": "./src/pill.css",
     "./forms.js": "./src/forms.js",
-    "./prefs.js": "./src/prefs.js",
+    "./prefs.js": "./src/prefs.ts",
     "./dom.js": "./src/dom.js",
     "./modal.js": "./src/modal.js",
     "./shadow-css.js": "./src/shadow-css.js",