fix(gui): preserve word-delete in chat input

[JSap0914]

Summary\n- skip the global Ctrl/Cmd+Backspace stop shortcut while focus is inside an input, textarea, or contenteditable editor\n- remove the TipTap Mod-Backspace interception so native word-delete can run during streaming\n- apply the same editable-target guard to pending tool-call keyboard shortcuts\n\nFixes #12924.\n\n## Verification\n- npm --prefix gui test -- src/util/isTextInputTarget.test.ts\n- npx prettier --check gui/src/util/index.ts gui/src/util/isTextInputTarget.test.ts gui/src/pages/gui/Chat.tsx gui/src/components/mainInput/Lump/LumpToolbar/LumpToolbar.tsx gui/src/components/mainInput/TipTapEditor/utils/editorConfig.ts\n- npm --prefix gui run lint -- src/util/index.ts src/util/isTextInputTarget.test.ts src/pages/gui/Chat.tsx src/components/mainInput/Lump/LumpToolbar/LumpToolbar.tsx src/components/mainInput/TipTapEditor/utils/editorConfig.ts

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