feat: switch from ttyd to real kitty via Xpra HTML5

Replaced the tmux+ttyd web terminal with actual kitty running through
Xpra's HTML5 streaming. Full GPU rendering, native kitty tabs/splits,
persistent sessions, and multi-client support.

config/kitty.conf

@@ -0,0 +1,52 @@
+# Sethian Terminal Theme
+font_family      JetBrains Mono
+font_size        11.0
+bold_font        auto
+italic_font      auto
+
+# Sethian colors - dark with orange accents
+foreground       #e0e0e0
+background       #0a0a0a
+background_opacity 0.95
+
+cursor           #D35400
+cursor_shape     beam
+
+selection_foreground #0a0a0a
+selection_background #D35400
+
+# Tab bar
+active_tab_foreground   #0a0a0a
+active_tab_background   #D35400
+inactive_tab_foreground #999999
+inactive_tab_background #1a1a1a
+tab_bar_style           powerline
+
+# Normal colors
+color0  #1a1a1a
+color1  #cc3333
+color2  #4e9a06
+color3  #D35400
+color4  #3465a4
+color5  #75507b
+color6  #06989a
+color7  #d3d7cf
+
+# Bright colors
+color8  #555753
+color9  #ef2929
+color10 #8ae234
+color11 #fce94f
+color12 #729fcf
+color13 #ad7fa8
+color14 #34e2e2
+color15 #eeeeec
+
+# Window
+window_padding_width 4
+confirm_os_window_close 0
+enable_audio_bell no
+
+# URL handling
+url_color #D35400
+url_style curly