feat(tui): redesign chrome with unified key hints and help overlay

Introduce one key-hint grammar across every view: bold key, dim label,
priority-ordered hints that drop from the end instead of ellipsizing.
The month footer becomes a single split status bar with a friendly
selected date, the '?' mega-line becomes a real keyboard shortcut
panel, and the editor, agenda, search, picker, detail, and delete
frames share the same chips. Notifications carry check/warning marks.
Adds a live PTY smoke test covering view interaction and terminal
state restoration on q and Ctrl-C exits.

src/tui/EventEditor.cpp

@@ -7,6 +7,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <ctime>
+#include <initializer_list>
 #include <random>
 #include <sstream>
 #include <stdexcept>
@@ -253,6 +254,49 @@ std::string horizontal_line(const int width, const std::string_view left,
     return result;
 }
 
+struct KeyHint {
+    std::string_view key;
+    std::string_view label;
+};
+
+int hints_width(const KeyHint* const hints, const std::size_t count)
+{
+    int width = 0;
+    for (std::size_t index = 0; index < count; ++index) {
+        if (index != 0) width += 3;
+        width += static_cast<int>(hints[index].key.size() + 1 + hints[index].label.size());
+    }
+    return width;
+}
+
+// Key bold, label dim, three spaces between hints; the plain layout is
+// identical with ANSI disabled. Hints drop from the end to fit.
+std::string render_hints(const std::initializer_list<KeyHint> hints, const int width,
+                         const bool ansi)
+{
+    std::size_t count = hints.size();
+    while (count > 0 && hints_width(hints.begin(), count) > width) --count;
+    std::string result;
+    for (std::size_t index = 0; index < count; ++index) {
+        if (index != 0) result += "   ";
+        result += style(std::string{hints.begin()[index].key}, "1", ansi);
+        result += ' ';
+        result += style(std::string{hints.begin()[index].label}, "2", ansi);
+    }
+    const int used = hints_width(hints.begin(), count);
+    if (used < width) result.append(static_cast<std::size_t>(width - used), ' ');
+    return result;
+}
+
+std::string hints_interior_line(const std::initializer_list<KeyHint> hints, const int width,
+                                const bool ansi)
+{
+    if (width <= 0) return {};
+    if (width == 1) return "│";
+    if (width <= 3) return interior_line({}, width);
+    return "│  " + render_hints(hints, width - 4, ansi) + "│";
+}
+
 } // namespace
 
 EventEditor::EventEditor(const Date selected_day)
@@ -440,8 +484,9 @@ std::string EventEditor::render(const int requested_width, const int requested_h
                            : editing_ ? "  NOCAL · EDIT APPOINTMENT"
                                       : "  NOCAL · NEW APPOINTMENT";
     lines.push_back(styled_interior_line(heading, width, "1", ansi));
-    lines.push_back(styled_interior_line("  Tab/↓ next  Shift-Tab/↑ back  Space toggle",
-                                         width, "2", ansi));
+    lines.push_back(hints_interior_line(
+        {{"Tab", "next field"}, {"Shift-Tab", "previous field"}, {"Space", "toggle"}},
+        width, ansi));
     lines.push_back(styled_interior_line(
         original_.time_basis == TimeBasis::zoned && !original_.time_zone.empty()
             ? "  Times shown in source zone: " + original_.time_zone
@@ -470,8 +515,10 @@ std::string EventEditor::render(const int requested_width, const int requested_h
     }
 
     lines.push_back(rule);
-    lines.push_back(interior_line(error_.empty() ? "  Ready" : "  ! " + error_, width));
-    lines.push_back(styled_interior_line("  Ctrl-S save    Esc cancel", width, "1", ansi));
+    lines.push_back(error_.empty()
+                        ? styled_interior_line("  Ready", width, "2", ansi)
+                        : styled_interior_line("  ! " + error_, width, "1;31", ansi));
+    lines.push_back(hints_interior_line({{"Ctrl-S", "save"}, {"Esc", "cancel"}}, width, ansi));
     lines.push_back(bottom);
 
     // Keep the active field visible on short terminals by selecting a window