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/components/shared/file-viewer-mobile.js

@@ -1,4 +1,5 @@
 import { html, nothing } from 'lit';
+import { t }             from '../../lib/i18n.js';
 import { FileViewerBase } from './file-viewer-base.js';
 
 /**
@@ -43,14 +44,14 @@ export class MobileFileViewerPage extends FileViewerBase {
       <div class="mobile-file-viewer">
         <div class="mobile-section-header">
           <span class="mobile-section-title">
-            <button class="chat-page-back" title="Back" @click=${() => this._back()}>
+            <button class="chat-page-back" title=${t('fv.back')} @click=${() => this._back()}>
               <i class="bi bi-arrow-left"></i>
             </button>
             <span class="fv-mobile-name" title=${this.path ?? ''}><bdi>${this._basename()}</bdi></span>
           </span>
           <span class="fv-header-actions">
             ${this._renderModeToggle('chat-page-back')}
-            <button class="chat-page-back" title="Download" @click=${() => this._download()}>
+            <button class="chat-page-back" title=${t('fv.download')} @click=${() => this._download()}>
               <i class="bi bi-download"></i>
             </button>
           </span>