Add WebSocket, Socket.IO, and MCP (HTTP) request protocols

[mbadaz]

Adds three new streaming/stateful request protocols plus the collection-management work that preceded them. None of these commits were on main yet, so this PR bundles all unmerged work.

Streaming protocols (WebSocket, Socket.IO, MCP)

A single multiplexed live channel underpins all three: the browser opens one WebSocket to /live, and many protocol sessions multiplex over it keyed by sessionId. The Node server owns every outbound connection, so {{variables}}, headers, auth, and the cookie jar apply just like HTTP requests. Each protocol is a driver behind a shared LiveDriver interface; an in-memory session manager enforces per-socket/global caps and a hard lifetime.

• WebSocket — open a ws/wss connection, with a live message log, composer, and reusable saved messages.
• Socket.IO — connect to a Socket.IO server (URL path = namespace, with a configurable engine.io handshake path, JSON auth payload, query params, and an events filter), emit named events with JSON args, and watch incoming events. Reusable saved emits.
• MCP (HTTP) — connect to an external MCP server over Streamable HTTP (reusing headers + auth), browse its tools, fill a tool's arguments via a form generated from its JSON Schema, call it, and view the result. STDIO transport is out of scope for now.

Earlier collection-management work (also unmerged)

• Folders inside collections, nestable to any depth (Postman-style), with their own scripts in the execution chain; Postman import preserves folder structure.
• Drag-and-drop to move requests/folders between folders and collections.
• Batch import of a whole folder of Postman exports.
• Saved responses: each request keeps its last 3 responses (gitignored local cache).
• Unsaved-changes prompt now only fires on tab close, not on navigation between requests.

Testing

• Server: npm run typecheck, npm run build, 69 tests pass — including new integration tests that drive each protocol end-to-end through /live against in-test echo servers (ws, socket.io, and an MCP StreamableHTTPServerTransport), plus persistence round-trips.
• Client: npm run typecheck, npm run build, 15 tests pass.
• Boot smoke: server starts clean; /api and the existing /mcp server endpoint unaffected by the /live upgrade handling.

Note: the React editors for the streaming protocols (ConnectionEditor, McpEditor, JsonSchemaForm) have no automated coverage and were verified manually.

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