fix(web): clear terminal on workspace change; disable Mac Option as Meta

- terminal: on workspaceId change call terminal.clear() and
  terminal.reset() so the previous workspace's scrollback is wiped
  before the new shell's output appears.
- terminal: set macOptionIsMeta: false. With the default (true),
  Mac Option+key sequences (e.g. Option+[ emits ESC) leak a literal
  0x1b into the shell's stdin, which crashes downstream REPLs like
  Python's with "invalid non-printable character U+001B".

web/src/components/terminal/TerminalPanel.tsx

@@ -38,6 +38,12 @@ export function TerminalPanel({ workspaceId }: TerminalPanelProps) {
       terminal = new Terminal({
         cursorBlink: true,
         convertEol: true,
+        // Prevent Mac Option+key from emitting ESC. Without this, typing
+        // Option+[ etc. leaks a literal 0x1b into the shell's stdin, which
+        // can break downstream programs that don't interpret escape
+        // sequences (e.g. Python's REPL reports "invalid non-printable
+        // character U+001B").
+        macOptionIsMeta: false,
         fontFamily:
           'Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace',
         fontSize: 12,
@@ -102,6 +108,10 @@ export function TerminalPanel({ workspaceId }: TerminalPanelProps) {
     hasWelcomedRef.current = false;
     isDeadRef.current = false;
     setIsDead(false);
+    // Clear the previous workspace's scrollback so the user does not see
+    // shell output from another workspace in the new one.
+    terminal.clear();
+    terminal.reset();
 
     const removeInputHandler = terminal.onData((input) => {
       if (!isDeadRef.current) {