feat: add Hermes Agent as 6th supported app type (Phase 1)

Register AppType::Hermes across the entire Rust backend:
- Add Hermes variant to AppType enum with additive mode and MCP support
- Add hermes field to McpApps, SkillApps, CommonConfigSnippets, and all
  per-app structs (McpRoot, PromptRoot, VisibleApps, AppSettings)
- Create minimal hermes_config.rs with get_hermes_dir() respecting
  settings override, matching the pattern of other app config modules
- Update all match arms in commands, services, deeplink, proxy, mcp,
  session_manager, and test files
- Extract shared build_additive_app_settings() to eliminate duplication
  between OpenClaw and Hermes deep link handling
- Combine identical OpenClaw/Hermes proxy match arms into unified arms

src-tauri/src/mcp/opencode.rs

@@ -259,6 +259,7 @@ pub fn import_from_opencode(config: &mut MultiAppConfig) -> Result<usize, AppErr
                         codex: false,
                         gemini: false,
                         opencode: true,
+                        hermes: false,
                     },
                     description: None,
                     homepage: None,