feat: make MCP restore command always available in Cmd+K

The "Install MCP Server" command was only enabled when status was
"not_installed", preventing users from re-registering when MCP got
removed or broken. Now the command is always available:
- Shows "Install MCP Server" when not installed
- Shows "Restore MCP Server" when already installed
- Added restore/fix/repair keywords for discoverability
- Context-aware toast: "installed" vs "restored"
- Menu bar label updated to "Restore MCP Server"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/menu.rs

@@ -331,7 +331,7 @@ fn build_vault_menu(app: &App) -> MenuResult {
     let view_changes = MenuItemBuilder::new("View Pending Changes")
         .id(VAULT_VIEW_CHANGES)
         .build(app)?;
-    let install_mcp = MenuItemBuilder::new("Install MCP Server")
+    let install_mcp = MenuItemBuilder::new("Restore MCP Server")
         .id(VAULT_INSTALL_MCP)
         .build(app)?;
     let reindex = MenuItemBuilder::new("Reindex Vault")