Can AI replace QuillBot?

Build me a local paraphrasing and grammar tool to replace QuillBot. Requirements:

- A local web page on localhost:5170: Node + Express, one textarea in, one output pane,
  buttons for Paraphrase, Summarize, Fix grammar, and a tone select (standard, formal,
  casual, shorter).
- Paraphrase, summarize, and tone modes call an LLM (Anthropic or OpenAI key in .env)
  with a fixed prompt per mode; stream the output.
- Grammar mode calls a local LanguageTool server and lists each issue with its suggested
  fix, click to apply. No LLM needed for grammar.
- A diff view between input and output with word-level highlights (the `diff` npm
  package).
- Every run saved to SQLite via better-sqlite3: timestamp, mode, input, output. A
  history page lists the last 100 with copy buttons.
- Cmd+Enter runs the selected mode.
- No accounts, no telemetry; text leaves my machine only for LLM calls, grammar checking
  stays fully local.
- Out of scope: browser and Word extensions, plagiarism and AI detection. This lives in
  one tab.
- README: LanguageTool setup (needs Java or Docker) and which API key to add.