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-base.js

@@ -2,6 +2,7 @@ import { html, nothing } from 'lit';
 import { unsafeHTML }     from 'lit/directives/unsafe-html.js';
 import { LightElement, renderMarkdown } from '../../lib/base.js';
 import { fileWatcher }    from '../../lib/file-watcher.js';
+import { t }              from '../../lib/i18n.js';
 
 /**
  * Shared file-viewer engine. Holds all of the fetch / kind-detection /
@@ -346,7 +347,7 @@ export class FileViewerBase extends LightElement {
     const showingSource = this._htmlMode === 'source';
     return html`<button
       class=${btnClass}
-      title=${showingSource ? 'Show preview' : 'Show source'}
+      title=${showingSource ? t('fv.mode_preview') : t('fv.mode_source')}
       @click=${() => this._toggleHtmlMode()}>
       <i class="bi ${showingSource ? 'bi-eye' : 'bi-code-slash'}"></i>
     </button>`;
@@ -389,7 +390,7 @@ export class FileViewerBase extends LightElement {
     if (this._kind === 'binary') {
       return html`<div class="fv-state text-muted">
         <i class="bi bi-file-earmark-binary fs-3 d-block mb-2"></i>
-        Preview not available for this file type.
+        ${t('fv.binary_unavailable')}
       </div>`;
     }
     if (this._kind === 'html') {
@@ -417,7 +418,7 @@ export class FileViewerBase extends LightElement {
       return html`
         ${this._compileError
           ? html`<details class="fv-compile-error">
-              <summary><i class="bi bi-exclamation-triangle text-warning"></i>&nbsp;LaTeX compilation failed — showing source instead</summary>
+              <summary><i class="bi bi-exclamation-triangle text-warning"></i>&nbsp;${t('fv.latex_failed')}</summary>
               <pre>${this._compileError}</pre>
             </details>`
           : nothing}