feat: Support 16-bit terminal themes (#146)

Add a terminal theme that inherits the terminal default background and uses the host terminal's 16-color ANSI palette for UI colors.

refs #140

4 files changed, 30 insertions, 32 deletions

diff --git a/src/app/state.rs b/src/app/state.rs
index 1a2bbddf..72630749 100644
--- a/src/app/state.rs
+++ b/src/app/state.rs
@@ -121,6 +121,28 @@ impl Palette {
         }
     }
 
+    /// Terminal 16-color theme.
+    pub fn terminal() -> Self {
+        Self {
+            accent: Color::Blue,
+            panel_bg: Color::Reset,
+            surface0: Color::Reset,
+            surface1: Color::DarkGray,
+            surface_dim: Color::DarkGray,
+            overlay0: Color::Gray,
+            overlay1: Color::White,
+            text: Color::Reset,
+            subtext0: Color::Gray,
+            mauve: Color::Gray,
+            green: Color::Green,
+            yellow: Color::Yellow,
+            red: Color::LightRed,
+            blue: Color::Blue,
+            teal: Color::Cyan,
+            peach: Color::Yellow,
+        }
+    }
+
     /// Tokyo Night — blue-purple aesthetic.
     pub fn tokyo_night() -> Self {
         Self {
@@ -456,6 +478,7 @@ impl Palette {
         match name.to_lowercase().replace([' ', '_'], "-").as_str() {
             "catppuccin" | "catppuccin-mocha" => Some(Self::catppuccin()),
             "catppuccin-latte" | "latte" | "light" => Some(Self::catppuccin_latte()),
+            "terminal" => Some(Self::terminal()),
             "tokyo-night" | "tokyonight" => Some(Self::tokyo_night()),
             "tokyo-night-day" | "tokyo-day" | "tokyonight-day" => Some(Self::tokyo_night_day()),
             "dracula" => Some(Self::dracula()),
@@ -615,6 +638,7 @@ impl SettingsSection {
 pub const THEME_NAMES: &[&str] = &[
     "catppuccin",
     "catppuccin-latte",
+    "terminal",
     "tokyo-night",
     "tokyo-night-day",
     "dracula",
diff --git a/src/config/theme.rs b/src/config/theme.rs
index 9d641862..87722b6e 100644
--- a/src/config/theme.rs
+++ b/src/config/theme.rs
@@ -5,7 +5,7 @@ use tracing::warn;
 ///
 /// ```toml
 /// [theme]
-/// name = "tokyo-night"  # built-in: catppuccin, tokyo-night, dracula, nord, etc.
+/// name = "tokyo-night"  # built-in: catppuccin, terminal, dracula, nord, etc.
 ///
 /// [theme.custom]        # override individual tokens on top of the base
 /// accent = "#f5c2e7"
diff --git a/src/main.rs b/src/main.rs
index 79a5d544..c1b0acd3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -61,8 +61,9 @@ const DEFAULT_CONFIG: &str = r##"# herdr configuration
 # onboarding = true
 
 [theme]
-# Built-in themes: catppuccin, tokyo-night, dracula, nord, gruvbox,
-#                  one-dark, solarized, kanagawa, rose-pine, vesper
+# Built-in themes: catppuccin, terminal, tokyo-night, dracula, nord,
+#                  gruvbox, one-dark, solarized, kanagawa, rose-pine,
+#                  vesper
 # name = "catppuccin"
 
 # Override individual color tokens on top of the base theme.
diff --git a/src/ui/panes.rs b/src/ui/panes.rs
index 971901bd..d9108575 100644
--- a/src/ui/panes.rs
+++ b/src/ui/panes.rs
@@ -1,6 +1,6 @@
 use ratatui::{
     layout::Rect,
-    style::{Color, Modifier, Style},
+    style::{Modifier, Style},
     text::{Line, Span},
     widgets::{Block, Borders, Paragraph},
     Frame,
@@ -293,10 +293,7 @@ pub(super) fn render_panes(app: &AppState, frame: &mut Frame, area: Rect) {
                 for y in inner.y..inner.y + inner.height {
                     for x in inner.x..inner.x + inner.width {
                         let cell = &mut buf[(x, y)];
-                        let style = cell.style();
-                        let fg = style.fg.unwrap_or(Color::White);
-                        let dimmed_fg = dim_color(fg);
-                        cell.set_style(style.fg(dimmed_fg));
+                        cell.set_style(cell.style().add_modifier(Modifier::DIM));
                     }
                 }
             }
@@ -313,30 +310,6 @@ pub(super) fn render_panes(app: &AppState, frame: &mut Frame, area: Rect) {
     }
 }
 
-/// Render selection highlight for a pane by inverting fg/bg colors.
-/// Reduce a color's brightness by blending it toward black.
-fn dim_color(color: Color) -> Color {
-    match color {
-        Color::Rgb(r, g, b) => Color::Rgb(r / 3, g / 3, b / 3),
-        Color::White => Color::DarkGray,
-        Color::Gray => Color::DarkGray,
-        Color::DarkGray => Color::Rgb(30, 30, 30),
-        Color::Red => Color::Rgb(60, 0, 0),
-        Color::Green => Color::Rgb(0, 60, 0),
-        Color::Yellow => Color::Rgb(60, 60, 0),
-        Color::Blue => Color::Rgb(0, 0, 60),
-        Color::Magenta => Color::Rgb(60, 0, 60),
-        Color::Cyan => Color::Rgb(0, 60, 60),
-        Color::LightRed => Color::Rgb(80, 30, 30),
-        Color::LightGreen => Color::Rgb(30, 80, 30),
-        Color::LightYellow => Color::Rgb(80, 80, 30),
-        Color::LightBlue => Color::Rgb(30, 30, 80),
-        Color::LightMagenta => Color::Rgb(80, 30, 80),
-        Color::LightCyan => Color::Rgb(30, 80, 80),
-        _ => Color::DarkGray,
-    }
-}
-
 fn render_selection_highlight(
     selection: &Option<crate::selection::Selection>,
     frame: &mut Frame,