fix(tui): re-query autocomplete picker on cursor movement

moveCursor() repositioned the cursor but never called updateAutocomplete()
or cancelAutocomplete(), unlike insertCharacter()/handleBackspace(). So an
open autocomplete picker went stale when the cursor moved: e.g. typing
`/cmd ` (argument menu open) then arrowing Left back into the command name
left the argument list showing against a `/cmd` prefix, and a Tab there
concatenated the stale suggestion onto the partial command name
(e.g. `/swarepo`).

Sync the picker at the end of moveCursor(): when a picker is open, re-query
via updateAutocomplete(), which refreshes the list for the new cursor
position or closes it when nothing matches.

Adds a regression test in test/editor.test.ts (verified to fail without the
fix). Fixes earendil-works/pi#5496.

packages/tui/src/components/editor.ts

@@ -1742,6 +1742,18 @@ export class Editor implements Component, Focusable {
 				}
 			}
 		}
+
+		// Keep an open autocomplete picker in sync with the new cursor
+		// position: cursor movement changes the text before the cursor, so a
+		// picker computed for the old position is stale. Re-query so it
+		// refreshes — or closes when the new position yields no suggestions —
+		// mirroring insertCharacter()/handleBackspace(). Without this, arrowing
+		// left from `/cmd ` back into the command name leaves the argument
+		// picker showing against a `/cmd` prefix (and a Tab there would
+		// concatenate the stale suggestion onto the partial command name).
+		if (this.autocompleteState) {
+			this.updateAutocomplete();
+		}
 	}
 
 	/**