feat: add interactive multi-turn chat REPL (mmx text repl) (#141)

* feat: add raw-mode line editor with bordered chrome for text repl

Introduce a custom LineEditor class for interactive terminal input that
renders a bordered input area using ANSI escape sequences. The editor
supports:

- Arrow key navigation (left/right/home/end)
- History browsing (up/down)
- Emacs-style line editing (Ctrl+A, Ctrl+E, Ctrl+U, Ctrl+W)
- Backspace and delete
- Raw-mode keypress handling with per-character processing

The text repl command skeleton wires the editor to stdin and provides
a minimal /exit command. Chat integration will follow.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add slash command system with real-time suggestion rendering

Wire up the slash command infrastructure in the text repl:

- Define 7 slash commands: /exit, /clear, /system, /model, /save, /help,
  /history
- Show filtered command suggestions below the input area in real time
  as the user types — no Tab key required
- Auto-hide suggestions when the command is fully typed or / is deleted
- Tab key auto-completes the only matching slash command
- handleSlash() dispatches typed commands to their handlers

The suggestion rendering reuses the LineEditor's existing ANSI layout,
appending matches below the bottom border outside the input area.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add conversation state and streaming chat API integration to repl

Wire the REPL to the MiniMax Messages API for real chat:

- Introduce ReplState to track messages, model, system prompt, and sampling
  parameters across turns
- Implement sendMessages() with SSE streaming, thinking/response display
  separation, and automatic conversation history accumulation
- Wire /clear, /system, /model, /save, and /history slash commands to
  operate on the live conversation state
- Add SIGINT handler with double-Ctrl+C to quit and single-interrupt
  during response streaming
- Initialize state from CLI flags (--model, --system, --temperature, etc.)
  and config defaults

The echo placeholder is replaced with a full chat loop — each user message
is added to the conversation, streamed to the API, and the assistant
response is appended back to history.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: register text repl command in command registry

Wire the text repl command into the CLI's command trie so it is
discoverable via `mmx text repl` and shown in help output under
`mmx text --help`.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add unit tests for text repl command

Verify command import, metadata, option flags, and non-interactive
mode rejection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: null-guard LineEditor.resolve before calling callback

When raw mode is enabled, stdin may flush buffered data before
readLine() is called, causing this.resolve to be null.

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Raylan LIN <linrion101@gmail.com>

Author: 3 people