feat: add mpv with ModernZ OSC as default video player

- mpv-modernz-git + mpv-thumbfast-git in aur.txt
- /etc/mpv/mpv.conf disables stock OSC + title bar
- /etc/mpv/script-opts/modernz.conf overrides colors to Catppuccin Mocha (lavender accent)
- moonarch-doctor checks deployed mpv configs

defaults/etc/mpv/mpv.conf

@@ -0,0 +1,5 @@
+# Disable stock OSC — ModernZ replaces it.
+osc=no
+
+# Hide native title bar for a cleaner borderless look (ModernZ draws its own).
+title-bar=no

defaults/etc/mpv/script-opts/modernz.conf

@@ -0,0 +1,32 @@
+# ABOUTME: ModernZ OSC overrides for moonarch — Catppuccin Mocha palette.
+# ABOUTME: Only keys that diverge from upstream defaults; Lua defaults fill the rest.
+
+# --- Background ---
+osc_color=#181825
+thumbnail_box_color=#11111b
+thumbnail_box_outline=#45475a
+
+# --- Text ---
+window_title_color=#cdd6f4
+window_controls_color=#cdd6f4
+title_color=#cdd6f4
+cache_info_color=#a6adc8
+time_color=#cdd6f4
+chapter_title_color=#cdd6f4
+
+# --- Buttons ---
+side_buttons_color=#cdd6f4
+middle_buttons_color=#cdd6f4
+playpause_color=#cdd6f4
+held_element_color=#6c7086
+
+# --- Accent (Lavender, matches waybar glow / swaync border) ---
+seekbarfg_color=#b4befe
+seekbarbg_color=#45475a
+seekbar_cache_color=#585b70
+seek_handle_color=#b4befe
+seek_handle_border_color=#cba6f7
+hover_effect_color=#b4befe
+nibble_color=#b4befe
+nibble_current_color=#cdd6f4
+nibbles_style=gap