feat(pool): an admin's switch moves a user's Claude login at once

PUT /api/accounts/pins (and agenthub accounts pin) now writes a pinned
Claude login into the user's home right away (claude-pool.switchHome):
every home's newer pair is copied back first, the member's own login is
never written over, and no pane is restarted — running sessions take the
new pair at their next credentials read. A live home stays on the login it
holds, so unpinning does not flip it back. The Users page calls it
"Switch a user's account" and says what happened.

client/src/i18n/locales/en/users.json

@@ -198,21 +198,24 @@
       "codex": "An OpenAI API key (sk-…), or the whole ~/.codex/auth.json after `codex login` with a ChatGPT account."
     },
     "refreshFailed": "refresh failed",
-    "pinned": "Pinned: {{users}}",
-    "pinUser": "Pin a user",
-    "pinTitle": "Pin a user to an account",
-    "pinHint": "That user's new sessions always run on the chosen account instead of the least-used one — even when it is full. Sessions already running keep their account; a login waits until the user's sessions on another login have ended.",
-    "pinButton": "Save pin",
+    "pinned": "Used by: {{users}}",
+    "pinUser": "Switch a user's account",
+    "pinTitle": "Switch a user's account",
+    "pinHint": "That user's sessions run on the chosen account instead of the least-used one — even when it is full. A Claude login is written into their home at once: sessions already running move to it at their next login check, with no restart. A setup-token or Codex account applies to new sessions.",
+    "pinButton": "Switch",
     "user": "User",
     "chooseUser": "Choose a user…",
     "loadingUsers": "Loading…",
     "pinAccount": "Account",
-    "noPin": "None — the least-used account",
-    "pinsTitle": "Pinned users",
-    "unpin": "Unpin {{name}}",
+    "noPin": "Automatic — the least-used account",
+    "pinsTitle": "Switched users",
+    "unpin": "Back to automatic for {{name}}",
     "pinDone": {
       "pinned": "{{user}} now runs on {{account}}",
-      "unpinned": "{{user}} is back on the least-used account"
+      "unpinned": "{{user}} is back on the least-used account",
+      "switched": "{{user}} switched to {{account}} — running sessions follow at their next login check",
+      "own-login": "{{user}} signed in with their own login, which was left alone",
+      "expired": "{{account}} has expired — {{user}}'s new sessions fall back to the least-used account"
     },
     "toolName": {
       "claude": "Claude",