feat: add MCP server support with global library and per-project toggles

Add Model Context Protocol (MCP) server configuration support. Users can
define MCP servers globally (new sidebar tab) and enable them per-project.
Enabled servers are injected into containers as MCP_SERVERS_JSON env var
and merged into ~/.claude.json by the entrypoint.

Backend: McpServer model, McpStore (JSON + atomic writes), 4 CRUD commands,
container injection with fingerprint-based recreation detection.
Frontend: MCP sidebar tab, McpPanel/McpServerCard components, useMcpServers
hook, per-project MCP checkboxes in ProjectCard config.

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

app/src-tauri/src/models/mcp_server.rs

@@ -0,0 +1,52 @@
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "snake_case")]
+pub enum McpTransportType {
+    Stdio,
+    Http,
+    Sse,
+}
+
+impl Default for McpTransportType {
+    fn default() -> Self {
+        Self::Stdio
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct McpServer {
+    pub id: String,
+    pub name: String,
+    #[serde(default)]
+    pub transport_type: McpTransportType,
+    pub command: Option<String>,
+    #[serde(default)]
+    pub args: Vec<String>,
+    #[serde(default)]
+    pub env: HashMap<String, String>,
+    pub url: Option<String>,
+    #[serde(default)]
+    pub headers: HashMap<String, String>,
+    pub created_at: String,
+    pub updated_at: String,
+}
+
+impl McpServer {
+    pub fn new(name: String) -> Self {
+        let now = chrono::Utc::now().to_rfc3339();
+        Self {
+            id: uuid::Uuid::new_v4().to_string(),
+            name,
+            transport_type: McpTransportType::default(),
+            command: None,
+            args: Vec::new(),
+            env: HashMap::new(),
+            url: None,
+            headers: HashMap::new(),
+            created_at: now.clone(),
+            updated_at: now,
+        }
+    }
+}