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/hooks/useMcpServers.ts

@@ -0,0 +1,55 @@
+import { useCallback } from "react";
+import { useShallow } from "zustand/react/shallow";
+import { useAppState } from "../store/appState";
+import * as commands from "../lib/tauri-commands";
+import type { McpServer } from "../lib/types";
+
+export function useMcpServers() {
+  const {
+    mcpServers,
+    setMcpServers,
+    updateMcpServerInList,
+    removeMcpServerFromList,
+  } = useAppState(
+    useShallow(s => ({
+      mcpServers: s.mcpServers,
+      setMcpServers: s.setMcpServers,
+      updateMcpServerInList: s.updateMcpServerInList,
+      removeMcpServerFromList: s.removeMcpServerFromList,
+    }))
+  );
+
+  const refresh = useCallback(async () => {
+    const list = await commands.listMcpServers();
+    setMcpServers(list);
+  }, [setMcpServers]);
+
+  const add = useCallback(
+    async (name: string) => {
+      const server = await commands.addMcpServer(name);
+      const list = await commands.listMcpServers();
+      setMcpServers(list);
+      return server;
+    },
+    [setMcpServers],
+  );
+
+  const update = useCallback(
+    async (server: McpServer) => {
+      const updated = await commands.updateMcpServer(server);
+      updateMcpServerInList(updated);
+      return updated;
+    },
+    [updateMcpServerInList],
+  );
+
+  const remove = useCallback(
+    async (id: string) => {
+      await commands.removeMcpServer(id);
+      removeMcpServerFromList(id);
+    },
+    [removeMcpServerFromList],
+  );
+
+  return { mcpServers, refresh, add, update, remove };
+}