Add a Generator page for server names, usernames, and passwords

New "Generator" nav item, open to every role since it's a pure
client-side utility with no data mutation. Three independent cards:
- Server name: picks from Swedish girl names or Disney characters (or
  both), skipping any name already used by an existing server —
  checked against the real server list, not just avoiding duplicates
  within one session.
- Username: adjective+animal with a configurable separator and an
  optional 2-digit suffix.
- Password: length slider, per-charset toggles, an "exclude ambiguous
  characters" option (0/O, 1/l/I), and a rough entropy/strength
  readout. Uses crypto.getRandomValues with rejection sampling (not
  Math.random or a plain modulo), since a biased password generator
  is a real security footgun.

Nothing generated here is sent to or stored on the server — it's
computed entirely in the browser and only reaches the backend if the
user pastes it into some other form themselves (e.g. Secrets, adding
a server).

Verified generators.ts directly: collision avoidance always returns
the one remaining unused name when every other option in a themed
list is taken, the full-list-exhausted fallback produces a numbered
name that still doesn't collide, matching is case-insensitive,
per-charset password generation only ever produces characters from
the selected sets, excludeAmbiguous holds across 200 40-character
samples, entropy math matches the expected log2 formula, and a
5000-sample single-character distribution came out uniform (469-521
per digit against an expected 500, no modulo bias) confirming the
rejection-sampling RNG is unbiased.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/layout/AppShell.tsx

@@ -21,6 +21,7 @@ import {
   IconMenu2,
   IconSun,
   IconMoon,
+  IconWand,
 } from "@tabler/icons-react";
 import type { CurrentUser } from "../api/client";
 import { getTheme, setTheme, type Theme } from "../utils/theme";
@@ -46,6 +47,7 @@ const NAV_ITEMS: NavItem[] = [
   { to: "/semaphore", label: "Semaphore", icon: <IconPlayerPlay size={20} /> },
   { to: "/gitea", label: "Gitea", icon: <IconBrandGit size={20} /> },
   { to: "/integrations", label: "Integrations", icon: <IconPlugConnected size={20} /> },
+  { to: "/generator", label: "Generator", icon: <IconWand size={20} /> },
   { to: "/users", label: "Users", icon: <IconUsers size={20} />, minRole: "admin" },
   { to: "/sessions", label: "Sessions", icon: <IconDevices size={20} />, minRole: "admin" },
   { to: "/audit-log", label: "Audit Log", icon: <IconHistory size={20} />, minRole: "operator" },