feat: TUI widget primitives (colors, InputField, draw helpers)

Implement COLOR_* constants, initialization, box/centered drawing,
clamp utility, and InputField with handle_key/value logic for pure
text editing without live curses. All tests pass.

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

openvpncertupdate.py

@@ -353,6 +353,106 @@ def send_email(
         )
 
 
+# ============================================================
+# === TUI WIDGETS ===
+# ============================================================
+
+COLOR_NORMAL   = 1
+COLOR_SELECTED = 2
+COLOR_DISABLED = 3
+COLOR_TITLE    = 4
+COLOR_ERROR    = 5
+COLOR_SUCCESS  = 6
+
+
+def init_colors() -> None:
+    curses.start_color()
+    curses.use_default_colors()
+    curses.init_pair(COLOR_NORMAL,   curses.COLOR_WHITE, -1)
+    curses.init_pair(COLOR_SELECTED, curses.COLOR_BLACK, curses.COLOR_CYAN)
+    curses.init_pair(COLOR_DISABLED, 8, -1)
+    curses.init_pair(COLOR_TITLE,    curses.COLOR_WHITE, -1)
+    curses.init_pair(COLOR_ERROR,    curses.COLOR_RED,   -1)
+    curses.init_pair(COLOR_SUCCESS,  curses.COLOR_GREEN, -1)
+
+
+def draw_box(win, title: str = "") -> None:
+    win.box()
+    if title:
+        _, w = win.getmaxyx()
+        label = f" {title} "
+        x = max(1, (w - len(label)) // 2)
+        try:
+            win.addstr(0, x, label, curses.color_pair(COLOR_TITLE) | curses.A_BOLD)
+        except curses.error:
+            pass
+
+
+def draw_centered(win, y: int, text: str, attr: int = 0) -> None:
+    _, w = win.getmaxyx()
+    x = max(0, (w - len(text)) // 2)
+    try:
+        win.addstr(y, x, text, attr)
+    except curses.error:
+        pass
+
+
+def clamp(value: int, lo: int, hi: int) -> int:
+    return max(lo, min(hi, value))
+
+
+class InputField:
+    """Single-line editable text field. draw() needs a live curses window;
+    handle_key() + value are pure logic."""
+
+    def __init__(
+        self, win, y: int, x: int, width: int,
+        initial: str = "", mask: bool = False,
+    ) -> None:
+        self._win   = win
+        self._y     = y
+        self._x     = x
+        self._width = width
+        self._mask  = mask
+        self._buf   = list(initial)
+        self._cur   = len(self._buf)
+
+    @property
+    def value(self) -> str:
+        return "".join(self._buf)
+
+    def draw(self) -> None:
+        display = ("*" * len(self._buf)) if self._mask else "".join(self._buf)
+        start   = max(0, self._cur - self._width + 1)
+        visible = display[start: start + self._width].ljust(self._width)
+        try:
+            self._win.addstr(self._y, self._x, visible,
+                             curses.color_pair(COLOR_NORMAL) | curses.A_UNDERLINE)
+            self._win.move(self._y, self._x + min(self._cur - start, self._width - 1))
+        except curses.error:
+            pass
+
+    def handle_key(self, key: int) -> None:
+        if key in (curses.KEY_BACKSPACE, 127, 8):
+            if self._cur > 0:
+                del self._buf[self._cur - 1]
+                self._cur -= 1
+        elif key == curses.KEY_LEFT:
+            self._cur = clamp(self._cur - 1, 0, len(self._buf))
+        elif key == curses.KEY_RIGHT:
+            self._cur = clamp(self._cur + 1, 0, len(self._buf))
+        elif key == curses.KEY_HOME:
+            self._cur = 0
+        elif key == curses.KEY_END:
+            self._cur = len(self._buf)
+        elif key == curses.KEY_DC:
+            if self._cur < len(self._buf):
+                del self._buf[self._cur]
+        elif 32 <= key <= 126:
+            self._buf.insert(self._cur, chr(key))
+            self._cur += 1
+
+
 # (remaining sections added in later tasks)
 # ============================================================