feat(settings): per-field scope tags + scope resolution (T-449)

Each settings field gains a scope tag showing where its value lives — folder
= Project (.clide), globe = Always (~/.clide), circle-dashed = Default/unset —
colour-coded (statusSuccess / statusWarning / muted) with a tooltip. Tapping
opens a menu to move the value between the scopes the key supports, or reset
to default; the tag's menu replaces the interim reset button.

Backs it with scope-explicit SettingsStore access — rawAt / setAt / removeAt /
effectiveLayer / writableLayers — over the two storage files (app ~/.clide,
project .clide). ext.* keys layer project-over-app; app.*/project.* keys live
only in their prefix's file, so their menu offers that one scope + reset.

Tests: store scope ops (layering, reload, guards) and the tag (Default vs
All-clide rendering, menu reset).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/kernel/src/i18n/catalog/builtin.settings-ui_en_us.json

@@ -3,5 +3,12 @@
   "modal.close": { "translation": "Close" },
   "modal.close.hint": { "translation": "Close settings without changing anything" },
   "rail.header": { "translation": "Categories" },
-  "panel.empty": { "translation": "No settings categories are registered yet." }
+  "panel.empty": { "translation": "No settings categories are registered yet." },
+  "scope.project": { "translation": "This project" },
+  "scope.always": { "translation": "All clide" },
+  "scope.default": { "translation": "Default" },
+  "scope.reset": { "translation": "Reset to default" },
+  "scope.tip.project": { "translation": "Stored in this project (.clide)" },
+  "scope.tip.always": { "translation": "Stored for all clide (~/.clide)" },
+  "scope.tip.default": { "translation": "Unset — using the default" }
 }