feat(settings): replicate the WorkBuddy appearance panel and dark theme (TODO 11)

Recover the WorkBuddy 5.8.3 appearance page from REA evidence (appearance-DMmhwsxq.css + tokens-Df-i-zsO.css): 44 recovered .appearance-* rules, scoped light/dark tokens, original geometry (panel [232,40,638,640], preview 634x317, grid 634x218.391, cards 118.797x79.188) and the two REA-exported preview images with provenance sha256.

Wire the panel into SettingsDialog with only the requested light/dark cards, add scoped tokens to the settings shell so the dark theme no longer renders a white window with near-white text, and verify with scripts/verify-appearance-settings.cjs (21 assertions: geometry, instant switch, cross-window sync, persistence, dark/light surface sampling with contrast >= 4.5, no renderer errors). Update the legacy nav/account/desktop appearance verifiers to the new .appearance-card selectors.

scripts/rea/probe-todo11-preview-media.json

@@ -0,0 +1,8 @@
+{
+  "include_fonts": false,
+  "include_message_content": false,
+  "media_selectors": [".appearance-preview__image"],
+  "actions": [
+    { "kind": "wait", "step_id": "preview-media", "duration_ms": 400, "frames": 0 }
+  ]
+}