Remove Phoenix & Notebooks — Phase 1: Decouple database shells to CloudShell (#2513)

* Add implementation plan for removing Phoenix and notebooks

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

* Phase 1: Decouple database shells from Phoenix to CloudShell-only

Migrate all shell terminals to the CloudShell path and remove the legacy Phoenix notebook-server terminal code so shells no longer depend on notebook provisioning.

- TerminalTab now always uses CloudShellTerminalComponentAdapter; removed the notebook-server adapter branch, getNotebookServerInfo, and the dead VCoreMongo firewall check
- Migrate Postgres and VCore Mongo quickstart tabs to CloudShellTerminalComponent (drop allocateContainer/useNotebook dependencies)
- Refactor useTerminal to send input via the CloudShell WebSocket instead of postRobot/iframe; register the socket from CloudShellTerminalComponent
- Simplify Explorer.openNotebookTerminal to always open a CloudShell terminal
- Delete NotebookTerminalComponent(+test/less/snapshot), NotebookTerminalComponentAdapter, and the src/Terminal/ entry point
- Remove the terminal.html webpack entry/HTML plugin and src/Terminal from tsconfig.strict.json

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

---------

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

webpack.config.js

@@ -111,7 +111,6 @@ module.exports = function (_env = {}, argv = {}) {
     index: "./src/Index.tsx",
     quickstart: "./src/quickstart.ts",
     hostedExplorer: "./src/HostedExplorer.tsx",
-    terminal: "./src/Terminal/index.ts",
     cellOutputViewer: "./src/CellOutputViewer/CellOutputViewer.tsx",
     selfServe: "./src/SelfServe/SelfServe.tsx",
     connectToGitHub: "./src/GitHub/GitHubConnector.ts",
@@ -128,11 +127,6 @@ module.exports = function (_env = {}, argv = {}) {
       template: "src/explorer.html",
       chunks: ["main"],
     }),
-    new HtmlWebpackPlugin({
-      filename: "terminal.html",
-      template: "src/Terminal/index.html",
-      chunks: ["terminal"],
-    }),
     new HtmlWebpackPlugin({
       filename: "quickstart.html",
       template: "src/quickstart.html",