feat(ui): add chat-driven dataset review flow

Move dataset review clarification into the assistant workspace and
rework the review page into a chat-centric layout with execution rails.

Add session-scoped assistant actions for mappings, semantic fields,
and SQL preview generation. Introduce optimistic locking for dataset
review mutations, propagate session versions through API responses,
and mask imported filter values before assistant exposure.

Refresh tests, i18n, and spec artifacts to match the new workflow.

BREAKING CHANGE: dataset review mutation endpoints now require the
X-Session-Version header, and clarification is no longer handled
through ClarificationDialog-based flows

frontend/src/components/TaskLogViewer.svelte

@@ -1,12 +1,8 @@
 <!-- [DEF:TaskLogViewer:Component] -->
 <!--
-@SIDE_EFFECT: None
 @UX_STATE: Loading -> Default
-@PRE: Default pre condition
-@POST: Default post condition
-@DATA_CONTRACT: Default state data
 
-@COMPLEXITY: 5
+@COMPLEXITY: 3
 @SEMANTICS: task, log, viewer, inline, realtime
 @PURPOSE: Displays task logs inline (in drawer) or as modal. Merges real-time WebSocket logs with polled historical logs.
 @LAYER: UI

frontend/src/components/auth/ProtectedRoute.svelte

@@ -1,11 +1,6 @@
 <!--[DEF:ProtectedRouteModule:Module] -->
 <!--
-@PRE: Default pre condition
-@DATA_CONTRACT: Default state data
-@SIDE_EFFECT: None
-@POST: Default post condition
-
-@COMPLEXITY: 5
+@COMPLEXITY: 3
 @SEMANTICS: auth, route-guard, permission, redirect, session-validation
 @PURPOSE: Enforces authenticated and authorized access before protected route content is rendered.
 @LAYER: UI