feat(web): rationalize settings IA into personal-preferences shell with admin rehoming [SPRINT-026]

Settings shell now owns only personal user preferences (appearance,
language, layout, AI assistant). All 14 admin/tenant/ops leaves
converted to controlled redirects pointing at their canonical owners
(Administration, Setup, Ops). Language merged into user-preferences.
Identity-providers rehomed from settings to administration as
canonical owner. Navigation config updated. 22 new route tests added.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/modules/ui/implementation_plan.md

@@ -7,6 +7,7 @@ Provide a living plan for UI deliverables, dependencies, and evidence.
 - Track current sprints under `docs/implplan/SPRINT_*.md` for this module.
 - Update this file when new scoped work is approved.
 - Sprint `025` is active for safe cleanup of approved dead leaves and committed generated/debug artifacts in the Web workspace.
+- Sprint `026` shipped Settings IA rationalization: the Settings shell now owns only personal preferences (appearance, language, layout, AI assistant). All admin, tenant, and operations configuration leaves redirect to their canonical owners (Administration, Setup, Ops). See `docs/features/checked/web/settings-ia-rationalization-ui.md`.
 
 ## Near-term deliverables
 - No active UI deliverables are currently staged in `docs/implplan`.