feat: custom kitty tab bar with system status + install scripts

Custom tab_bar.py with flat tabs, right-aligned status area (git branch,
CPU%, memory, uptime, hostname, clock) using Nerd Font icons. F12/Shift+F12
toggle for tab bar. Added Kitty-setup.md, theme-setup.md, and install
scripts for kitty-only and full Debian theme deployment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

install-debian-theme.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Install the full Seth Linux Theme on Debian/Ubuntu with GNOME
+set -euo pipefail
+
+TARGET_HOME="${1:-$HOME}"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+echo "=== Seth Linux Theme — Full Install ==="
+echo "Target: $TARGET_HOME"
+echo ""
+
+# ── GTK CSS ──
+echo "--- GTK CSS ---"
+mkdir -p "$TARGET_HOME/.config/gtk-3.0" "$TARGET_HOME/.config/gtk-4.0"
+cp "$SCRIPT_DIR/gtk-3.0/gtk.css" "$TARGET_HOME/.config/gtk-3.0/gtk.css"
+cp "$SCRIPT_DIR/gtk-3.0/gtk.css" "$TARGET_HOME/.config/gtk-4.0/gtk.css"
+echo "[ok] GTK3/4 CSS installed."
+
+# ── Kitty ──
+echo ""
+echo "--- Kitty Terminal ---"
+if command -v kitty &>/dev/null; then
+    bash "$SCRIPT_DIR/install-kitty-theme.sh" "$TARGET_HOME"
+else
+    echo "[skip] kitty not found. Install kitty first, then run:"
+    echo "       $SCRIPT_DIR/install-kitty-theme.sh $TARGET_HOME"
+fi
+
+# ── GNOME Settings ──
+echo ""
+echo "--- GNOME Settings ---"
+if command -v gsettings &>/dev/null; then
+    bash "$SCRIPT_DIR/gnome/apply-gnome-settings.sh"
+else
+    echo "[skip] gsettings not found — not a GNOME session?"
+fi
+
+echo ""
+echo "=== Install complete ==="
+echo "  - GTK apps: open new windows to see changes (libadwaita apps need full relaunch)"
+echo "  - Kitty: restart kitty"
+echo "  - GNOME: changes applied immediately"