feat(themes): add color derivation and themed app templates

Add script/omarchy-theme-color and expand omarchy-theme-set-templates to
derive a full palette from each theme's colors.toml, then render new
themed templates (shell, pi, vscode theme, gum, neovim, claude, hermes,
t3code) from it.

Adds backgrounds and palette updates for existing themes plus new themes
(last-horizon, lupine, solitude, tidewater-*, miasma, ...).

themes/tidewater-dark/colors.toml

@@ -0,0 +1,35 @@
+# Tidewater Dark
+# Deep-teal night palette: teal water, coral light, warm sand.
+# Companion to tidewater-light; same hues, mirrored lightness.
+
+mode = "dark"
+
+accent = "#5cc9c1"
+selection = "#26403e"
+muted = "#47605e"
+
+background = "#0e1a1a"
+dark_background = "#0a1414"
+darker_background = "#060e0e"
+lighter_background = "#1a2b2a"
+
+foreground = "#d3e3e0"
+dark_foreground = "#6d8784"
+light_foreground = "#a4bfbc"
+bright_foreground = "#eef7f5"
+
+red = "#e57f6d"
+yellow = "#e3c07b"
+orange = "#e0996a"
+green = "#8fcaa4"
+cyan = "#5cc9c1"
+blue = "#74a9cf"
+magenta = "#cf8fb0"
+brown = "#9c7358"
+
+bright_red = "#f0937f"
+bright_yellow = "#f0d093"
+bright_green = "#a6dcb8"
+bright_cyan = "#7ad9d1"
+bright_blue = "#8fbfe0"
+bright_magenta = "#e0a6c6"