fix TUI crash on serial consoles; make index.txt the sole email store

curses.use_default_colors() raises on terminals (e.g. serial consoles
using TERM=linux/vt100) whose terminfo lacks default-color support;
init_colors() now falls back to an explicit black background and caps
the "disabled" color to 8-color terminals.

--reissue without --email silently sent no mail when the CN wasn't in
openvpncertupdate-metadata.json, even though its email was already
embedded in the cert's index.txt subject (via EASYRSA_REQ_EMAIL) and
the TUI already fell back to it. Since build_client_full() always
writes that subject field whenever an email is known, metadata.json
was a redundant, driftable copy — remove it and have get_email() read
index.txt directly, picking the last non-revoked entry for a CN since
index.txt can contain revoked/duplicate lines for the same CN.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_widgets.py

@@ -1,4 +1,4 @@
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, patch
 import curses as _curses
 
 # Stub just enough of the curses API for InputField to import
@@ -12,7 +12,7 @@ _curses.KEY_HOME     = 262
 _curses.KEY_END      = 360
 _curses.KEY_DC       = 330
 
-from openvpncertupdate import InputField, clamp
+from openvpncertupdate import InputField, clamp, init_colors, COLOR_NORMAL, COLOR_DISABLED
 
 
 def _field(initial="", mask=False):
@@ -51,3 +51,34 @@ def test_clamp_bounds():
     assert clamp(5, 0, 10) == 5
     assert clamp(-1, 0, 10) == 0
     assert clamp(11, 0, 10) == 10
+
+
+def _init_colors_calls(*, use_default_colors_raises, colors):
+    calls = []
+    use_default = MagicMock(
+        side_effect=_curses.error("use_default_colors() returned ERR")
+        if use_default_colors_raises else None
+    )
+    with patch.object(_curses, "start_color"), \
+         patch.object(_curses, "use_default_colors", use_default), \
+         patch.object(_curses, "init_pair", side_effect=lambda *a: calls.append(a)), \
+         patch.object(_curses, "COLORS", colors, create=True):
+        init_colors()
+    return calls
+
+def test_init_colors_uses_default_colors_when_supported():
+    calls = _init_colors_calls(use_default_colors_raises=False, colors=256)
+    normal = next(c for c in calls if c[0] == COLOR_NORMAL)
+    disabled = next(c for c in calls if c[0] == COLOR_DISABLED)
+    assert normal[2] == -1
+    assert disabled[1:] == (8, -1)
+
+def test_init_colors_falls_back_on_serial_console():
+    # Serial consoles (e.g. TERM=linux/vt100) often lack the terminfo
+    # "op"/"AX" capability, so use_default_colors() raises curses.error
+    # and only 8 colors are available.
+    calls = _init_colors_calls(use_default_colors_raises=True, colors=8)
+    normal = next(c for c in calls if c[0] == COLOR_NORMAL)
+    disabled = next(c for c in calls if c[0] == COLOR_DISABLED)
+    assert normal[2] == _curses.COLOR_BLACK
+    assert disabled[1:] == (_curses.COLOR_WHITE, _curses.COLOR_BLACK)