Add share target, prompt templates, command palette and session organisation

- PWA share target: shared text/links start a new chat or go into a
  recent session (chooser dialog)
- Prompt templates (personal + global for admins) with {{placeholders}}
  that are asked for on insert; managed under Settings → Templates
- Ctrl/Cmd+K command palette; Alt+N new session, Alt+Up/Down switch
  sessions, Ctrl+, settings
- Sessions can be pinned, archived and filed into folders; the list can
  be grouped by date or by project, groups are collapsible
- Fix: the "What's new" dialog was never shown to signed-in users

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/components/Settings.tsx

@@ -11,6 +11,7 @@ import { applyTheme, getTheme, getThemeMode, onThemeChange, THEME_MODES, THEMES,
 import { setReasoningMode, useReasoningMode, type ReasoningMode } from "../prefs";
 import { ModelSelect } from "./ModelSelect";
 import { Account } from "./settings/Account";
+import { Templates } from "./settings/Templates";
 import { AgentsEditor } from "./settings/AgentsEditor";
 import { Folders } from "./settings/Folders";
 import { Users } from "./settings/Users";
@@ -923,8 +924,8 @@ function Raw({ reload }: { reload: () => void }) {
 
 // --- page -------------------------------------------------------------------
 
-const ADMIN_TABS = ["general", "providers", "agents", "mcp", "permissions", "users", "folders", "tools", "audit", "account", "raw"] as const;
-const USER_TABS = ["general", "account"] as const;
+const ADMIN_TABS = ["general", "providers", "agents", "mcp", "permissions", "users", "folders", "tools", "audit", "templates", "account", "raw"] as const;
+const USER_TABS = ["general", "templates", "account"] as const;
 const TAB_ICONS: Record<string, string> = {
   general: "gear",
   providers: "brain",
@@ -935,6 +936,7 @@ const TAB_ICONS: Record<string, string> = {
   folders: "folders",
   tools: "toolbox",
   audit: "scroll",
+  templates: "template",
   account: "user",
   raw: "file-text",
 };
@@ -970,6 +972,7 @@ export function Settings({ tab, onMenu }: { tab?: string; onMenu: () => void })
           {isAdmin && !cfg && !error && <div className="empty">{t("common.loading")}</div>}
           {!isAdmin && active === "general" && <InterfaceSettings />}
           {active === "account" && <Account />}
+          {active === "templates" && <Templates />}
           {cfg && active === "users" && <Users />}
           {cfg && active === "folders" && <Folders />}
           {cfg && active === "audit" && <Audit />}