redbear-power: add nord, gruvbox, solarized-dark themes (6 total)

New theme presets selectable via --theme:
  nord           cyan borders, light-blue governor
  gruvbox        green borders, yellow governor
  solarized-dark blue borders, magenta governor

Help text updated with all 6 theme names.

local/recipes/system/redbear-power/source/src/render.rs

@@ -2044,7 +2044,8 @@ OPTIONS:
                      Requires redbear-sessiond to be running. If the
                      session bus is not reachable, the TUI continues
                      without D-Bus (a warning is printed to stderr).
-    --theme MODE     Color theme: dark (default), light, high-contrast.
+    --theme MODE     Color theme: dark (default), light, high-contrast,
+                     nord, gruvbox, solarized-dark.
                      Overrides [theme].mode in the config file.
     --config PATH    Load configuration from PATH instead of the
                      standard locations. The file must be valid TOML.

local/recipes/system/redbear-power/source/src/theme.rs

@@ -58,6 +58,9 @@ impl Theme {
         match mode {
             "light" => Self::light(),
             "high-contrast" => Self::high_contrast(),
+            "nord" => Self::nord(),
+            "gruvbox" => Self::gruvbox(),
+            "solarized-dark" => Self::solarized_dark(),
             _ => Self::dark(),
         }
     }
@@ -88,6 +91,33 @@ impl Theme {
             cursor_highlight: Style::new().white().on_black().bold(),
         }
     }
+
+    pub fn nord() -> Self {
+        Self {
+            border_focused: Style::new().cyan().bold(),
+            border_dim: Style::new().dark_gray(),
+            header_governor: Style::new().light_blue().bold(),
+            cursor_highlight: Style::new().bold(),
+        }
+    }
+
+    pub fn gruvbox() -> Self {
+        Self {
+            border_focused: Style::new().green().bold(),
+            border_dim: Style::new().dark_gray(),
+            header_governor: Style::new().yellow().bold(),
+            cursor_highlight: Style::new().bold(),
+        }
+    }
+
+    pub fn solarized_dark() -> Self {
+        Self {
+            border_focused: Style::new().blue().bold(),
+            border_dim: Style::new().dark_gray(),
+            header_governor: Style::new().magenta().bold(),
+            cursor_highlight: Style::new().bold(),
+        }
+    }
 }
 
 impl Default for Theme {