feat(desktop): per-workspace MCP client config installer

Add commands to register the gateway endpoint in a project-local MCP config
inside a chosen folder, injecting `X-Mcpmux-Workspace: <folder path>` so the
gateway routes the connection to that folder's workspace binding without
relying on the client reporting MCP roots.

- list_workspace_install_clients: the supported project-local clients
  (Cursor, Claude Code, VS Code/Copilot, opencode, Zed) with their config
  paths. Each client's config-shape differences (top-level key mcpServers /
  servers / mcp / context_servers, and the type field) live in one table.
- generate_workspace_config_snippet: copy-paste full-file snippet per client.
- install_workspace_mcp_config: create or extend each client's config,
  preserving other servers, backing up an existing file, creating parent
  dirs. Refuses to clobber a non-JSON (JSONC) file, reporting it instead.

Global-only clients (Windsurf, Cline) and Claude Desktop (stdio, no static
headers) are excluded — a per-workspace header needs project-local scope.

Tested: entry shape per client, merge create/extend/replace, preserve
siblings, reject JSONC/non-object, create-then-update-with-backup on disk.

Claude-Session: https://claude.ai/code/session_01Baan9JmzR43uxxRUh7CAMF
Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

apps/desktop/src-tauri/src/commands/mod.rs

@@ -21,6 +21,7 @@ pub mod server_manager;
 pub mod settings;
 pub mod space;
 pub mod workspace_binding;
+pub mod workspace_install;
 
 // Re-export commands for convenience
 pub use builtin_servers::*;
@@ -40,3 +41,4 @@ pub use server_manager::*;
 pub use settings::*;
 pub use space::*;
 pub use workspace_binding::*;
+pub use workspace_install::*;