Major rebranding, i18n, dashboard, shared folders, role capabilities

- Rebrand: new app/agent icons, SKALD.md, warm "paper" CSS palette
  (terracotta accent, --radius tokens, WCAG contrast, reduced-motion),
  updated favicon, tray icon, skaldkonur asset
- i18n: backend crate (i18n.rs, locale column, ui_locale config),
  frontend library (web/lib/i18n.js, I18nMixin, t(key)),
  translation files (web/i18n/), every component wired
- Dashboard: <dashboard-page> replaces old home-page content;
  <app-copilot> becomes the landing page (full/dock layout modes)
- Shared folders: API endpoints (shared_folders.rs), frontend page,
  can_write membership, container mount topology, user_fs routing
- Role capabilities: new db table & authorization seam (data not enums),
  roles.attrs JSON for ui_mode / interface select
- Setup: skald-setup prompts for language + password, sets ui_locale
- General: components migrated to CSS variables, Lit conventions cleanup,
  connectors/catalog/marketplace/approval refactoring

web/index.html

@@ -93,6 +93,7 @@
       <agents-page></agents-page>
       <users-page></users-page>
       <roles-page></roles-page>
+      <shared-folders-page></shared-folders-page>
       <connectors-page></connectors-page>
       <connector-detail-page></connector-detail-page>
       <marketplace-page></marketplace-page>
@@ -104,7 +105,7 @@
       <approval-groups-page></approval-groups-page>
       <approval-rules-page></approval-rules-page>
       <config-page></config-page>
-      <home-page></home-page>
+      <dashboard-page></dashboard-page>
       <agent-inbox-page></agent-inbox-page>
       <llm-requests-page></llm-requests-page>
       <session-detail-page style="display:none"></session-detail-page>