feat(themes): full revision of executive-slate — palette rebuild + real whole-swap bar

The executive-slate preset shipped a waybar.css that referenced @base/@accent
with no @define-color block, and no matching waybar.jsonc — so the raw-read
override ran a largely unstyled bar (the item-28 partial-whole-swap defect).
The palette was also flat (base->surface only 1.13x) with a dim accent
(#4D78CC, 3.91 on base).

- Palette: widen surface stepping (base->surface 1.13x -> 1.29x so panels/
  selection/hover separate), brighten the accent (#4D78CC -> #5A8AE6, 3.91 ->
  5.04 on base, now AA text), lift subtext/good/warn/bad a tier, realign ansi,
  soften bright-white (#FFFFFF -> #F0F3F9). text stays 12.5 AAA. Contrast
  checker: all 23 themes x 7 pairings pass.
- Waybar: complete the bespoke bar as a real whole-swap. New waybar.jsonc with
  the full 17-module set (parity with summer-day/night); waybar.css rewritten
  to lead with its own @define-color block and cover every module + state class
  the helper scripts emit (.recording/.activated/.on/.available/.dnd-*/battery).
  Identity: solid, edge-to-edge, sharp corners, accent underline on the active
  workspace.
- Rofi: drop the broken var() idiom for the house *{}/@name convention (split
  border syntax, message/textbox/scrollbar elements for the theme-grid picker).
- CONVENTIONS: Waybar parity rule now names executive-slate as a third
  whole-swap target (was stale at summer-only).

V1: nix flake check --no-build green; strict JSON parse of both files; real
rofi parsed the .rasi cleanly; with executive-slate set active, the module
eval resolves waybar.settings -> the jsonc, waybar.style -> the css, rofi.theme
-> the override rasi, and theme.nix accepts the palette. NOT yet done: on-screen
render of the bar/rofi/desktop (V2/V3) and preview.png (deferred to on-hardware
capture, per the chosen path).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/CONVENTIONS.md

@@ -43,8 +43,8 @@ those, it probably shouldn't exist.
 - **Waybar:** new indicators self-gate (hidden when irrelevant), use
   named `writeShellScriptBin`s on PATH (so static configs can exec them
   by bare name), and are added to **both** the generated `waybar.nix`
-  config **and** the summer-day/night `waybar.jsonc` whole-swaps (the
-  parity rule).
+  config **and** every `waybar.jsonc` whole-swap — summer-day, summer-night
+  and executive-slate (the parity rule).
 - **Theming:** every new visual surface consumes the palette from the
   state JSON. There is no second renderer to keep in sync — add the key
   to the JSON, consume it in the module.