feat: implement Hermes MCP sync module (Phase 4)

Add mcp/hermes.rs with bidirectional MCP format conversion:
- convert_to_hermes_format: strip type field, infer from command/url
- convert_from_hermes_format: infer type, strip Hermes-specific fields
- Merge-on-write: existing Hermes fields (tools, sampling, timeout,
  roots, enabled) preserved when user has customized them
- update_mcp_servers_yaml: closure-based read-modify-write under write
  lock to prevent TOCTOU races in concurrent sync operations
- 9 unit tests for format conversion and merge logic

Wire up all MCP service dispatch:
- Replace Hermes TODO stubs with real sync/remove calls
- Remove Hermes from sync_all_enabled skip list
- Enable deep link hermes MCP flag (apps.hermes = true)
- Add Hermes import to import_mcp_from_apps command

src-tauri/src/mcp/mod.rs

@@ -9,10 +9,12 @@
 //! - `codex` - Codex MCP 同步和导入（含 TOML 转换）
 //! - `gemini` - Gemini MCP 同步和导入
 //! - `opencode` - OpenCode MCP 同步和导入（含 local/remote 格式转换）
+//! - `hermes` - Hermes MCP 同步和导入
 
 mod claude;
 mod codex;
 mod gemini;
+mod hermes;
 mod opencode;
 mod validation;
 
@@ -28,6 +30,7 @@ pub use gemini::{
     import_from_gemini, remove_server_from_gemini, sync_enabled_to_gemini,
     sync_single_server_to_gemini,
 };
+pub use hermes::{import_from_hermes, remove_server_from_hermes, sync_single_server_to_hermes};
 pub use opencode::{
     import_from_opencode, remove_server_from_opencode, sync_single_server_to_opencode,
 };