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>

src/hooks/useTerminal.ts

@@ -1,26 +1,20 @@
-import postRobot from "post-robot";
 import create, { UseStore } from "zustand";
 
 interface TerminalState {
-  terminalWindow: Window;
-  setTerminal: (terminalWindow: Window) => void;
+  socket: WebSocket | undefined;
+  setSocket: (socket: WebSocket | undefined) => void;
   sendMessage: (message: string) => void;
 }
 
 export const useTerminal: UseStore<TerminalState> = create((set, get) => ({
-  terminalWindow: undefined,
-  setTerminal: (terminalWindow: Window) => {
-    set({ terminalWindow });
+  socket: undefined,
+  setSocket: (socket: WebSocket | undefined) => {
+    set({ socket });
   },
   sendMessage: (message: string) => {
-    const terminalWindow = get().terminalWindow;
-    postRobot.send(
-      terminalWindow,
-      "sendMessage",
-      { type: "stdin", content: [message] },
-      {
-        domain: window.location.origin,
-      },
-    );
+    const socket = get().socket;
+    if (socket && socket.readyState === WebSocket.OPEN) {
+      socket.send(message + "\r");
+    }
   },
 }));