feat(apple): styling pass — dark-mode accent, recent-host state, glass HUD, security-sheet polish

Working through the brand-color follow-ups:

- AccentColor gains a dark-appearance variant (#8678F5 — the brand violet lifted one
  step toward the icon's light periwinkle) so tinted controls keep contrast on dark.
- Host cards remember sessions: StoredHost.lastConnected (set when a session reaches
  streaming) renders as a "Connected … ago" relative-time line, and the most recent
  host's card carries a subtle accent ring — the grid finally has hierarchy.
- The HUD swaps the pre-glass black-50% rectangle for .regularMaterial with an accent
  live-dot; hint lines use semantic .secondary instead of opacity.
- Security moments: the trust card's lock.shield and the pairing sheet's header take
  the brand tint; the PIN field is larger monospaced and uses the number pad on iOS.

Icon ↔ accent decision: the accent stays the exact brand #6656F2; the Icon Composer
layers keep their adjacent palette (#6C5BF3 family) — close enough to read as one
brand, and the icon remains the design-tool source of truth.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/App/Assets.xcassets/AccentColor.colorset/Contents.json

@@ -11,6 +11,24 @@
         }
       },
       "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0xF5",
+          "green" : "0x78",
+          "red" : "0x86"
+        }
+      },
+      "idiom" : "universal"
     }
   ],
   "info" : {