feat: Ghost Shell v2 — AGS v3 statusbar + violet-chaton v2 palette

- AGS v3.1.0 (Astal/GTK3) Ghost Shell avec ghost mode (heartbeat + hover reveal)
- Modules : clock, battery, volume (interactif), network, MPRIS, CPU/RAM, systray
- Brain Power panel (Super + B) — lecture live focus/todos/session
- tetardtek_ prompt avec curseur clignotant
- Palette violet-chaton v2 documentée (Mitsuri Kanroji gradient magenta → green)
- Autostart COSMIC via .desktop
- Archive AGS v1 conservée pour référence

ags-v3/styles/_palette.scss

@@ -0,0 +1,35 @@
+// ── violet-chaton v2 ──────────────────────────────────────────────────────
+// Mitsuri Kanroji inspired — gradient magenta → green
+// Ghost Shell edition
+
+// backgrounds
+$crust:     #1a0e27;
+$base:      #261537;
+$mantle:    #341c4a;
+$surface0:  #3d2454;
+$surface1:  #493161;
+$surface2:  #5a3875;
+
+// accents
+$magenta:   #ff4da6;
+$lilac:     #c9a0ff;
+$mitsuri:   #9adba8;
+$lavande:   #a4b4ff;
+$champagne: #e8c87a;
+$danger:    #f25c7a;
+
+// text
+$text:      #f0eaf8;
+$subtext1:  #c4b8d4;
+$subtext0:  #9a8fad;
+$muted:     #716686;
+
+// shared
+$font:      "Maple Mono NF", "MapleMono Nerd Font", monospace;
+$radius:    14px;
+$radius-sm: 8px;
+$transition: 300ms ease-out;
+
+// Note: alpha() is a GTK CSS function, not SCSS.
+// Use it raw in GTK CSS values, not in SCSS variables.
+// For SCSS variables that need transparency, use rgba().