feat(profiles): include Claude Desktop provider in project profiles

Claude Desktop's only dimension managed by cc-switch is its provider
(MCP/Skills are hardcoded unsupported and prompts have no live file),
so snapshots capture just the current desktop provider while the empty
MCP/Skills sets and None prompt make apply a natural no-op for the
other dimensions - no per-dimension special casing needed.

- Add claude-desktop slot to PROFILE_APPS and PerApp (serde key uses
  the hyphenated app id); old payloads without the key deserialize to
  None and leave Claude Desktop untouched on apply
- Gate the tray Projects submenu by iterating PROFILE_APPS instead of
  hardcoding Claude/Codex visibility
- Show the profile switcher on the Claude Desktop tab, mirror the
  PerApp type, invalidate the claude-desktop providers cache on apply,
  and extend the switcher tooltip in all four locales
- Extend the roundtrip integration test with the desktop provider
  dimension; the desktop switch is cfg-gated to macOS/Windows because
  desktop live writes error on Linux where CI runs cargo test

src/lib/api/profiles.ts

@@ -5,6 +5,7 @@ import { invoke } from "@tauri-apps/api/core";
  */
 export interface PerApp<T> {
   claude: T;
+  "claude-desktop": T;
   codex: T;
 }