add MCP developer tool with multi-unit support

First developer tool for the XDJ-100SX project. Connects Claude Code
directly to the Pi over SSH — push skin files, take screenshots, restart
Mixxx, flash Pico firmware, and more without leaving the editor.

Available MCP tools:
- run_command, read_file, write_file, list_files
- push_skin, pull_skin, push_skin_file, pull_skin_file
- push_midi, pull_midi
- take_screenshot, navigate_panel
- restart_mixxx
- check (preflight: SSH, Mixxx, Pico, audio)
- pico_bootloader, pico_flash
- discover_units — scan network for all reachable XDJ Pi units
- select_unit — switch active connection mid-session (multi-unit support)

Also adds --about flag and TUI About modal with authors and credits,
and fixes scrolling/close behavior on Help and About modals.

By: Jeancarlo Cardoso de Faria Filho (jaianlab) <jaianlabworks@gmail.com>

tools/xdj_pi_dev/_terminal.py

@@ -0,0 +1,158 @@
+from __future__ import annotations
+
+"""
+Shared terminal UI helpers.
+
+Extracted from xdj-pi-dev.py so all sub-modules can import consistent
+colour, spinner, and logging primitives without circular dependencies.
+"""
+
+import itertools
+import shutil
+import sys
+import threading
+from typing import Any
+
+
+# ─── ANSI colour ─────────────────────────────────────────────────────────────
+
+def _ansi_enable() -> bool:
+    """Enable ANSI on Windows; return True if terminal supports colour."""
+    if not sys.stdout.isatty():
+        return False
+    if sys.platform == "win32":
+        try:
+            import ctypes
+            k = ctypes.windll.kernel32
+            k.SetConsoleMode(k.GetStdHandle(-11), 7)
+        except Exception:
+            return False
+    return True
+
+
+_COLOR = _ansi_enable()
+
+
+class _C:
+    RESET  = "\033[0m"   if _COLOR else ""
+    BOLD   = "\033[1m"   if _COLOR else ""
+    DIM    = "\033[2m"   if _COLOR else ""
+    GREEN  = "\033[32m"  if _COLOR else ""
+    YELLOW = "\033[33m"  if _COLOR else ""
+    RED    = "\033[31m"  if _COLOR else ""
+    CYAN   = "\033[36m"  if _COLOR else ""
+    GRAY   = "\033[90m"  if _COLOR else ""
+    ERASE  = "\r\033[K"  if _COLOR else "\r"
+
+
+_SPIN_FRAMES = "⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏"
+
+
+# ─── Spinner step ─────────────────────────────────────────────────────────────
+
+class Step:
+    """
+    Context manager for a named operation with a live spinner.
+
+        with Step("Stopping Mixxx"):
+            pi_client.exec("killall mixxx")
+
+    Prints  ⠹  Stopping Mixxx...   while running,
+    then    ✓  Stopping Mixxx       on success,
+    or      ✗  Stopping Mixxx       on exception.
+    """
+
+    def __init__(self, label: str, indent: int = 2) -> None:
+        self.label  = label
+        self.indent = " " * indent
+        self._stop  = threading.Event()
+        self._thread: threading.Thread | None = None
+
+    def __enter__(self) -> "Step":
+        self._stop.clear()
+        self._thread = threading.Thread(target=self._spin, daemon=True)
+        self._thread.start()
+        return self
+
+    def _spin(self) -> None:
+        for frame in itertools.cycle(_SPIN_FRAMES):
+            sys.stdout.write(
+                f"{_C.ERASE}{self.indent}{_C.CYAN}{frame}{_C.RESET}"
+                f"  {self.label}…"
+            )
+            sys.stdout.flush()
+            if self._stop.wait(0.08):
+                break
+
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        self._stop.set()
+        if self._thread:
+            self._thread.join()
+        if exc_type is None:
+            sys.stdout.write(
+                f"{_C.ERASE}{self.indent}{_C.GREEN}✓{_C.RESET}"
+                f"  {self.label}\n"
+            )
+        else:
+            sys.stdout.write(
+                f"{_C.ERASE}{self.indent}{_C.RED}✗{_C.RESET}"
+                f"  {self.label}  {_C.DIM}({exc_val}){_C.RESET}\n"
+            )
+        sys.stdout.flush()
+        return False  # don't suppress exceptions
+
+
+# ─── Log routing ──────────────────────────────────────────────────────────────
+
+# Set by XDJApp when TUI is active; (level, msg) -> None  where level in ok/warn/fail/info/head
+_tui_log_fn: Any = None
+
+
+def section(title: str) -> None:
+    if _tui_log_fn:
+        _tui_log_fn("head", title)
+        return
+    w = shutil.get_terminal_size((72, 24)).columns
+    bar = "─" * min(w, 72)
+    print(f"\n{_C.BOLD}{bar}{_C.RESET}")
+    print(f"  {_C.BOLD}{title}{_C.RESET}")
+    print(f"{_C.BOLD}{bar}{_C.RESET}")
+
+
+def ok(msg: str) -> None:
+    if _tui_log_fn:
+        _tui_log_fn("ok", msg)
+        return
+    print(f"  {_C.GREEN}✓{_C.RESET}  {msg}")
+
+
+def warn(msg: str) -> None:
+    if _tui_log_fn:
+        _tui_log_fn("warn", msg)
+        return
+    print(f"  {_C.YELLOW}⚠{_C.RESET}  {msg}")
+
+
+def fail(msg: str) -> None:
+    if _tui_log_fn:
+        _tui_log_fn("fail", msg)
+        return
+    print(f"  {_C.RED}✗{_C.RESET}  {msg}")
+
+
+def _log_line(line: str) -> None:
+    lo = line.lower()
+    if _tui_log_fn:
+        if any(x in lo for x in ("error:", "fatal error:", " error ")):
+            _tui_log_fn("fail", line)
+        elif "warning:" in lo:
+            _tui_log_fn("warn", line)
+        elif line.strip():
+            _tui_log_fn("info", line)
+        return
+    if any(x in lo for x in ("error:", "fatal error:", " error ")):
+        print(f"  {_C.RED}│{_C.RESET} {_C.RED}{line}{_C.RESET}")
+    elif "warning:" in lo:
+        print(f"  {_C.YELLOW}│{_C.RESET} {_C.YELLOW}{line}{_C.RESET}")
+    elif line.strip():
+        print(f"  {_C.GRAY}│{_C.RESET} {line}")