feat: workspaces own their sessions; desktop parity; sidebar and settings cleanup

Workspace sessions (docs/plans/desktop-parity, phases 1-5 and 7):
- sessions.lane_id: a workspace lists only the sessions its panes held,
  stamped by bindRunSession (first writer wins, nested `claude -p`
  excluded); GET /api/sessions?lane=&archived=
- session row state dot, double-click rename, archive (sessions.archived_at,
  hides only); the activity bar's duplicate Sessions tab removed
- Fork beside Resume (--fork-session, Claude only), Ctrl/Cmd+click a live
  session opens it in a second pane, a diff line's comment is pasted into
  the workspace's last-focused pane (lib/panePaste.ts)

dashboard_runs stability:
- a pane's previous run is archived as <pane>@<started_at> instead of being
  overwritten by INSERT OR REPLACE
- a run is flagged abandoned only once its tmux session is gone, at boot and
  on the run-heal beat (panes outlive a server restart)

UI:
- sidebar: no footer, language or theme block; small collapse button in the
  brand corner; version + update check in the connection details modal, a
  status-bar dot while a release is out; language in Settings -> General
- one Switch component for every switch, the themed Checkbox for every
  checkbox (no native checkboxes)

Also: AI Tools catalog trimmed to 10 built-ins (custom-file prompt modes
tested through fixtures), and the workspace plans under docs/plans/ (the
multi-user server plan lives in the AgentHub-Server repo).

client/src/pages/Settings.tsx

@@ -55,6 +55,7 @@
  *
  * ----------------------------------------------------------------------------- */
 
+import { Checkbox } from "../components/Checkbox";
 import { useEffect, useState, useCallback } from "react";
 import { useTranslation } from "react-i18next";
 import {
@@ -108,6 +109,7 @@ import { Skeleton } from "../components/Skeleton";
 import { AlertsNotifications } from "../components/AlertsNotifications";
 import {
   SettingsRow,
+  SettingsSection,
   SettingsSegmented,
   SettingsSwitchRow,
 } from "../components/settings/SettingsRow";
@@ -194,7 +196,7 @@ export function Settings({
   /** Which of the two Settings pages this renders (`/settings/general` or `/settings/notifications`). */
   section?: "general" | "notifications";
 } = {}) {
-  const { t } = useTranslation("settings");
+  const { t, i18n } = useTranslation("settings");
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const [totalCost, setTotalCost] = useState<number | null>(null);
@@ -414,6 +416,23 @@ export function Settings({
 
       {section === "general" && (
         <>
+          <SettingsSection title={t("language.title")} description={t("language.description")}>
+            <SettingsRow
+              label={t("language.label")}
+              control={
+                <SettingsSegmented
+                  ariaLabel={t("language.label")}
+                  value={(i18n.resolvedLanguage ?? i18n.language).startsWith("vi") ? "vi" : "en"}
+                  onChange={(v) => void i18n.changeLanguage(v)}
+                  options={[
+                    { value: "en" as const, label: t("language.names.en") },
+                    { value: "vi" as const, label: t("language.names.vi") },
+                  ]}
+                />
+              }
+            />
+          </SettingsSection>
+
           {/* Cost summary card */}
           <div className="card p-6">
             <div className="flex items-center justify-between flex-wrap gap-4">
@@ -453,14 +472,11 @@ export function Settings({
 
             <div className="card p-5 space-y-4">
               <div className="flex items-center justify-between flex-wrap gap-3">
-                <label className="flex items-center gap-2 text-xs text-fg-secondary">
-                  <input
-                    type="checkbox"
-                    checked={gcDryRun}
-                    onChange={(e) => setGcDryRun(e.target.checked)}
-                  />
-                  {t("lanesSection.dryRun")}
-                </label>
+                <Checkbox
+                  checked={gcDryRun}
+                  onChange={setGcDryRun}
+                  label={t("lanesSection.dryRun")}
+                />
                 <button
                   onClick={handleGc}
                   disabled={actionLoading !== null}