fix(theme): solid per-theme hyprland borders, matching legacy

v1 forced an accent→accentAlt 45deg gradient on every theme's window
border; the legacy identity themes all used a *solid* border — accent for
nord/retro-82/lumon, the text tone for kanagawa/summer-day/summer-night.

Add a palette-resolved `border` field ({active, inactive}, each a palette
key or literal hex) to the theme schema with accent/overlay defaults in
theme.nix, consume it solid in hyprland.nix, and declare it in every
preset (and the live state). Declaring it everywhere is required because
`nomarchy-theme-sync apply` deep-merges presets — an omitted field would
stick across switches, like colors already are fully specified per theme.

All six identity themes resolve to their exact legacy active border
(verified: nord #81a1c1, retro-82 #faa968, lumon #f2fcff, kanagawa
#dcd7ba, summer-night #d3c6aa, summer-day #5c6a72). nix flake check passes.

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

themes/nord.json

@@ -18,6 +18,10 @@
     "warn": "#ebcb8b",
     "bad": "#bf616a"
   },
+  "border": {
+    "active": "accent",
+    "inactive": "overlay"
+  },
   "ansi": [
     "#3b4252",
     "#bf616a",