feat: add unified Settings sheet, MCP indicator, and Docker host config

- Add AppSettingsSheet (gear icon in Toolbar) with MCP, Docker, and AI sections
- MCP Server: toggle on/off, port config, status badge, endpoint URL with copy
- Docker: local/remote daemon selector with remote URL input
- AI: moved Ollama settings into the unified sheet
- MCP status probes actual TCP port for reliable running detection
- Docker commands respect configurable docker host (-H flag) for remote daemons
- MCP server supports graceful shutdown via tokio watch channel
- Settings persisted to app_settings.json alongside existing config files
- StatusBar shows MCP indicator (green/gray dot) with tooltip

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

src-tauri/src/models/settings.rs

@@ -0,0 +1,60 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AppSettings {
+    pub mcp: McpSettings,
+    pub docker: DockerSettings,
+}
+
+impl Default for AppSettings {
+    fn default() -> Self {
+        Self {
+            mcp: McpSettings::default(),
+            docker: DockerSettings::default(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct McpSettings {
+    pub enabled: bool,
+    pub port: u16,
+}
+
+impl Default for McpSettings {
+    fn default() -> Self {
+        Self {
+            enabled: true,
+            port: 9427,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct DockerSettings {
+    pub host: DockerHost,
+    pub remote_url: Option<String>,
+}
+
+impl Default for DockerSettings {
+    fn default() -> Self {
+        Self {
+            host: DockerHost::Local,
+            remote_url: None,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum DockerHost {
+    Local,
+    Remote,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct McpStatus {
+    pub enabled: bool,
+    pub port: u16,
+    pub running: bool,
+}