docs: document file-based router migration (frontend routing rewrite)
Rewrite the frontend routing documentation for the TanStack Router
file-based system (PR #1447) and record the migration with reasoning:
- architecture/frontend/Routing.md: full rewrite — request flow,
router bootstrap + defaults, single Register + staticData typing,
auth/status gate, role tiers, beforeLoad flag gates (fail-closed
trade-off documented), 404 split, redirect-after-login, route-owned
search state (#1238), loaders, navigation conventions, nav
projection, Vite codegen, add-a-route and add-a-flag walkthroughs;
4 validated mermaid diagrams
- codes/frontend/routes: RouteGuards rewritten for pathless layouts +
beforeLoad (HOC guidance removed); RoutesIndex rewritten as the
verified 29-route catalog
- changes/refactors: new dated migration entry with self-contained
reasoning for every design decision
- stale old-router references corrected across Feature-Flags,
Authentication, Roles, Frontend Structure/Overview, ReportingUnitBlockDetails,
Formula pages, LayoutSideNav, and index/log files; the deleted
search-params sync hook converted to a removal record
- block details accuracy: the route keeps its dedicated
reporting-unit-block-details-enabled flag (beforeLoad, same pattern
as RU details); its lack of role restriction predates the migration
(#1254 dropped the D9-era ADMIN gate on 2026-10-13) — preserved
1:1, not changed by the migration
docs: document block details feature flag
docs: update block details docs for route restructure
Rename the block details route to /reporting-units/$ruId/$blockId, document the new ReportingUnitBlocksList section on the reporting unit details page, and trim the standalone block details page doc to match the restructured implementation (decision D8).
docs: add reporting unit block details page docs
Documents ReportingUnitBlockDetailsPage, BlockDetailsSummary,
BlockDetailsSkeleton, useDelayedFlag, and useReportingUnitDetailsQuery;
updates routing, architecture overview, and frontend testing pages
(issue #1369, slices 1/2/4/5).