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

crates/skald-core/src/i18n.rs

@@ -0,0 +1,55 @@
+//! UI localization knobs.
+//!
+//! The instance default locale lives in the registry `config` table under
+//! [`DEFAULT_LOCALE_KEY`], editable by the admin from the Settings page. Each
+//! user can override it on their own profile (`users.locale`); the frontend
+//! resolves user → instance → built-in English at boot.
+
+use core_api::{ConfigProperty, ConfigSet, PropertyType};
+
+pub const DEFAULT_LOCALE_KEY: &str = "ui_locale";
+
+/// Locales the web UI ships dictionaries for. Anything else is rejected at
+/// write time (profile override, first-run setup) rather than silently
+/// falling back to English later.
+pub const SUPPORTED_LOCALES: &[&str] = &["en", "it", "fr"];
+
+pub fn is_supported(locale: &str) -> bool {
+    SUPPORTED_LOCALES.contains(&locale)
+}
+
+/// Writes the instance default locale straight to the registry `config` table.
+/// Used by first-run provisioning shells (e.g. `skald-setup`), where no
+/// `GlobalConfigManager` — hence no system bus — exists. A running server
+/// should go through `GlobalConfigManager::set` instead, which also emits the
+/// change event.
+pub async fn set_default_locale(pool: &sqlx::SqlitePool, locale: &str) -> anyhow::Result<()> {
+    anyhow::ensure!(is_supported(locale), "unsupported locale: {locale}");
+    sqlx::query(
+        "INSERT INTO config (key, value, updated_at) VALUES (?, ?, datetime('now'))
+         ON CONFLICT(key) DO UPDATE SET
+             value      = excluded.value,
+             updated_at = excluded.updated_at",
+    )
+    .bind(DEFAULT_LOCALE_KEY)
+    .bind(locale)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+pub fn config_set() -> ConfigSet {
+    ConfigSet {
+        name:        "Interface".into(),
+        description: "Look and feel of the web interface.".into(),
+        properties:  vec![
+            ConfigProperty {
+                key:           DEFAULT_LOCALE_KEY.into(),
+                name:          "Language".into(),
+                description:   "Default interface language for the whole instance (e.g. en, it). Each user can override it on their profile.".into(),
+                property_type: PropertyType::String,
+                default_value: Some("en".into()),
+            },
+        ],
+    }
+}