feat(theming): settings-store, nav merge util and radius tokens

Phases 0-2 of docs/website/THEMING_AND_NAV.md. Groundwork only: no admin UI,
no consumer wiring, and an instance that never touches the new settings keys
renders exactly as it does today.

Phase 0 - settings store:
- settingsDb.remove() and DELETE /api/v1/admin/settings/:key, the "reset to
  default" primitive. Defaults for these keys live in BRAND_* env, theme.css
  and the hardcoded NAV arrays, so reset has to delete the row rather than
  store a copy of the default. Allowlisted to the five theming/nav keys plus
  hero_layout_draft, admin-only, idempotent.
- GET /api/v1/settings/nav behind requireAuth with no role gate. AdminLayout
  renders for editors and moderators and PlayerPortalLayout for players, and
  none of them can read GET /admin/settings, so without this their nav
  override would silently never apply.
- A fifth router group for it: /public is anonymous, /admin/settings is
  adminOnly, /player is self-scoped data. This is configuration that needs a
  login.
- parseJsonSetting() in utils/settingsJson.js. settings.value is TEXT, so
  every JSON key arrives as a string; malformed or wrong-shaped reads as
  absent, never as an error and never half-applied.
- theme_visual / brand_assets / nav_public join PUBLIC_KEYS; nav_admin and
  nav_player deliberately do not.

Phase 1 - client/src/lib/navOverrides.js, the pure merge util. Presentation
only: it can set label/order/hidden and (grouped navs) group, and nothing
else. It cannot introduce a `to`, cannot touch roles/feature, and hidden:false
cannot un-hide anything - the existing filters run afterward, unchanged, and
remain the boundary.

Phase 2 - promoted 23 border-radius literals in theme.css to four tokens at
today's values (14x8px, 4x999px, 4x10px, 1x12px). The 7px/6px editor chrome
and the two 50% circles stay literal. --shadow-card and --panel-grad were
already tokens.

Tests: 16 new server tests, 20 new client tests. The route-manifest guard now
also asserts /settings/** sits behind requireAuth. Swagger and both route
artifacts regenerated.

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

server/src/router/v1/admin/settings.router.js

@@ -41,5 +41,22 @@ settingsRouter.put(
   adminOnly,
   ctrl.updateSettings,
 )
+// Reset one setting to its default by deleting the row. Only the keys whose
+// default lives outside the store (theming, nav, hero draft) are deletable —
+// the controller holds the allowlist.
+settingsRouter.delete(
+  '/:key',
+  // #swagger.tags = ['Admin · Settings']
+  // #swagger.summary = 'Reset one setting to its default (admin only)'
+  // #swagger.description = 'Deletes the settings row so the surface falls back to its BRAND_* env / theme.css / hardcoded default. Restricted to the resettable keys (theme_visual, brand_assets, nav_public, nav_admin, nav_player, hero_layout_draft). Idempotent: resetting a key that was never set succeeds.'
+  // #swagger.security = [{ "cookieAuth": [] }, { "bearerAuth": [] }]
+  /* #swagger.parameters['key'] = { in: 'path', required: true, description: 'Settings key to reset', schema: { type: 'string' } } */
+  /* #swagger.responses[200] = { description: 'Setting reset', content: { "application/json": { schema: { $ref: "#/components/schemas/Message" } } } } */
+  /* #swagger.responses[400] = { description: 'Setting is not resettable', content: { "application/json": { schema: { $ref: "#/components/schemas/Error" } } } } */
+  /* #swagger.responses[401] = { description: 'Not authenticated', content: { "application/json": { schema: { $ref: "#/components/schemas/Error" } } } } */
+  /* #swagger.responses[403] = { description: 'Admin role required', content: { "application/json": { schema: { $ref: "#/components/schemas/Error" } } } } */
+  adminOnly,
+  ctrl.deleteSetting,
+)
 
 module.exports = settingsRouter