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/file-viewer-page.js

@@ -1,4 +1,5 @@
 import { html, nothing } from 'lit';
+import { t }            from '../lib/i18n.js';
 import { FileViewerBase } from './shared/file-viewer-base.js';
 
 const PAGE_ID = 'file_viewer';
@@ -58,14 +59,14 @@ export class FileViewerPage extends FileViewerBase {
       <div class="llm-page fv-page">
         <div class="llm-page-header">
           <div class="llm-header-left">
-            <button class="btn btn-sm btn-outline-secondary back-btn" title="Back" @click=${() => this._back()}>
+            <button class="btn btn-sm btn-outline-secondary back-btn" title=${t('fv.back')} @click=${() => this._back()}>
               <i class="bi bi-arrow-left"></i>
             </button>
             <h2 class="llm-page-title fv-title" title=${this._path ?? ''}><bdi>${this._path ?? ''}</bdi></h2>
           </div>
           <div class="fv-header-actions">
             ${this._renderModeToggle('btn btn-sm btn-outline-secondary fv-download-btn')}
-            <button class="btn btn-sm btn-outline-secondary fv-download-btn" title="Download" @click=${() => this._download()}>
+            <button class="btn btn-sm btn-outline-secondary fv-download-btn" title=${t('fv.download')} @click=${() => this._download()}>
               <i class="bi bi-download"></i>
             </button>
           </div>