Remove Phoenix & Notebooks - Phase 2: Remove in-app notebook authoring & rendering (#2515)

Delete the nteract rendering engine, notebook tabs, panes, the read-only viewer, Schema Analyzer (pulled forward from Phase 3), and all UI entry points that open notebooks. Decouple surviving files (Explorer, NotebookManager, useNotebook, ResourceTreeAdapter) with minimal edits, keeping GitHub/Juno/Phoenix wiring for later phases.

Removed 22 zero-importer notebook-only npm deps; re-added phantom transitively-hoisted deps still used by surviving code: xterm, xterm-addon-fit (CloudShell), d3-collection (Graph), @nteract/myths (@nteract/core).

Verified: compile, compile:strict, lint (0 errors), format:check, test (1945 passing), build:ci all green.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

webpack.config.js

@@ -4,8 +4,6 @@ require("dotenv/config");
 const path = require("path");
 const MonacoWebpackPlugin = require("monaco-editor-webpack-plugin");
 const HtmlWebpackPlugin = require("html-webpack-plugin");
-const InlineChunkHtmlPlugin = require("react-dev-utils/InlineChunkHtmlPlugin");
-const HTMLInlineCSSWebpackPlugin = require("html-inline-css-webpack-plugin").default;
 const { EnvironmentPlugin } = require("webpack");
 const MiniCssExtractPlugin = require("mini-css-extract-plugin");
 const CopyWebpackPlugin = require("copy-webpack-plugin");
@@ -111,7 +109,6 @@ module.exports = function (_env = {}, argv = {}) {
     index: "./src/Index.tsx",
     quickstart: "./src/quickstart.ts",
     hostedExplorer: "./src/HostedExplorer.tsx",
-    cellOutputViewer: "./src/CellOutputViewer/CellOutputViewer.tsx",
     selfServe: "./src/SelfServe/SelfServe.tsx",
     connectToGitHub: "./src/GitHub/GitHubConnector.ts",
     redirectBridge: "./src/redirectBridge.ts",
@@ -142,11 +139,6 @@ module.exports = function (_env = {}, argv = {}) {
       template: "src/hostedExplorer.html",
       chunks: ["hostedExplorer"],
     }),
-    new HtmlWebpackPlugin({
-      filename: "cellOutputViewer.html",
-      template: "src/CellOutputViewer/cellOutputViewer.html",
-      chunks: ["cellOutputViewer"],
-    }),
     new HtmlWebpackPlugin({
       filename: "connectToGitHub.html",
       template: "src/connectToGitHub.html",
@@ -196,10 +188,6 @@ module.exports = function (_env = {}, argv = {}) {
       filename: "[name].[contenthash].css",
     }),
     ...htmlWebpackPlugins,
-    new InlineChunkHtmlPlugin(HtmlWebpackPlugin, [/cellOutputViewer/]),
-    new HTMLInlineCSSWebpackPlugin({
-      filter: (fileName) => fileName.includes("cellOutputViewer"),
-    }),
     new MonacoWebpackPlugin(),
     new CopyWebpackPlugin({
       patterns: [