unify color palette, harden shikane service, misc sway/opencode updates

sway:
- config: re-apply shikane profile after every reload
  (exec_always shikanectl reload); restart waybar on reload
  (exec_always pkill+waybar); enable default_border pixel 2;
  add tlpctl power-saver at startup
- keybinds: disable floating_modifier (was "$mod normal") -
  experiment for windows popping out via accidental mod+click
- windows: case-insensitive pydm title match for floating rule
- swayfx + waybar style: unified 5-color palette (base00-0F) with
  doc headers; waybar theme restyled to match the sway palette
- waybar config: scratchpad module in left bar, "S{count}" format
- new quickshell shell.qml bar

systemd user units:
- shikane.service: bind to graphical-session/sway-session targets,
  Type=simple, Restart=on-failure (2s) with start limits so crashes
  recover without giving up permanently
- new sway-session.target and its wants/ symlinks

opencode:
- load AGENTS.md as instructions (new file)
- move OpenWebUI API key from hardcoded to {env:OPENWEBUI_API_KEY}

.config/sway/waybar/config.jsonc

@@ -4,6 +4,7 @@
     "modules-left": [
         "sway/workspaces",
         "sway/submap",
+        "sway/scratchpad",
         "sway/window"
     ],
     //"modules-center": [
@@ -22,7 +23,7 @@
         "format": "<span style=\"italic\">{}</span>"
     },
     "sway/scratchpad": {
-        "format": "{count}",
+        "format": "S{count}",
         "show-empty": false,
         "tooltip": true,
         "tooltip-format": "{app}: {title}"