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/session/handler/mod.rs

@@ -20,7 +20,7 @@ use crate::config::DatetimeConfig;
 use crate::db::{chat_history, chat_sessions_stack};
 use crate::events::ServerEvent;
 use core_api::message_meta::MessageMetadata;
-use core_api::user_fs::UserFs;
+use core_api::user_fs::SharedFs;
 use crate::llm::LlmManager;
 use crate::mcp::McpProvider;
 use crate::image_generate::ImageGeneratorManager;
@@ -272,8 +272,11 @@ pub struct ChatSessionHandler {
     pub(super) user_id:          String,
     /// The owner's filesystem view (home + shared folders + container), threaded
     /// into every [`ToolContext`] so disk fs-tools resolve per-user host paths and
-    /// `execute_cmd` execs into the owner's container (blueprint §6).
-    pub(super) fs:               Arc<UserFs>,
+    /// `execute_cmd` execs into the owner's container (blueprint §6). A **shared
+    /// swappable cell** (not a snapshot): a shared-folder membership change is
+    /// applied in place (§6 remount), so a live session picks it up on its next
+    /// tool call without being rebuilt — see [`SharedFs`].
+    pub(super) fs:               SharedFs,
     pub(super) llm_manager:      Arc<LlmManager>,
     pub(super) max_history_messages:  usize,
     pub(super) max_tool_rounds:       usize,
@@ -343,7 +346,7 @@ impl ChatSessionHandler {
         db:                    Arc<SqlitePool>,
         shared_pool:           Arc<SqlitePool>,
         user_id:               String,
-        fs:                    Arc<UserFs>,
+        fs:                    SharedFs,
         llm_manager:           Arc<LlmManager>,
         max_history_messages:  usize,
         max_tool_rounds:       usize,