feat(in-page-nav): convert the six information routes onto the shared header

docs/codebase-index.md

@@ -329,7 +329,8 @@ One shared composer (`master-search-header.tsx`) serves every mode. Placement:
 - **Result and detail views**: fixed bottom dock on phone (compact variant on submitted searches), sticky top from `sm` up.
 - **Results routing**: standalone routes own their submitted searches via `?q=…&run=1` (`/services` → `ServicesNavigatorPage`, `/forms` → `FormsSearchResultsPage`, `/differentials` → `DifferentialsHome` results view, `/formulation` → local mechanism results, `/favourites` filters the command library in place). Answer, Documents, and Prescribing submitted searches render inside `ClinicalDashboard` — intentional, since they need retrieval/answer state. Bare `/?mode=<id>` always renders the shared home with that mode preselected; only a submitted deep link (`q` plus `run=1`) resolves to the mode's own search surface (proxy early-redirect still covers favourites/differentials/specifiers for those submitted aliases).
 - **Intentionally composer-free routes**: `/differentials/presentations/*` and `/differentials/compare` (comparison workflow owns its chrome), `/documents/[id]` viewer (has its own in-document ask composer), `/documents/source/*` (document flow owns mobile chrome). Do not re-flag these in search-consistency audits.
-- **Shared secondary navigation**: `src/components/secondary-navigation.tsx` (`SecondaryNavigation`, route/section/action items, roving tablist, fragment section tracking) and `src/components/page-secondary-navigation.tsx` (`PageSecondaryNavigation`, per-route selection of mode destinations vs. "On this page" section anchors). Mode destinations come from `src/lib/mode-secondary-navigation.ts` (`modeSecondaryNavigationRegistry`, no "Home" item). `GlobalSearchShell` renders it in normal flow at the top of `#main-content` for its owned namespaced modes; it self-suppresses on clean mode homes, locally-owned detail routes (medications, factsheets, differentials diagnoses) and Therapy Compass, and Specifiers/Formulation keep their existing local `Subnav` (so the shared mode bar is skipped for those two modes to avoid a duplicate row).
+- **Shared in-page navigation**: `src/components/in-page-nav/` is the default template for section navigation on any mode page (`docs/search-chrome-behaviour.md`). `in-page-nav-header.tsx` (`InPageNavHeader`) owns the header row, both sheets and the `PhoneHeaderCollapsePortal` wrapper; `page-section-index.ts` (`PageSection`, `toDocumentSections`, `sectionTargetIds`) is the declaration shape; `use-resolved-page-sections.ts` narrows a declaration to the anchors actually rendered at this breakpoint; `use-in-page-section-nav.ts` composes that with `useDocumentSectionSpy` and `jumpToDocumentSection`; `use-page-section-weights.ts` measures segment weights; `use-in-page-chrome-metrics.ts` publishes `--inpage-anchor-offset`; `in-page-nav-classes.ts` holds the shared anchor (`inPageAnchor`) and actions-sheet row classes. Anchor measurement itself is `src/components/sticky-chrome-metrics.ts` (`useStickyChromeMetrics`), shared with the document viewer's `use-document-chrome-metrics.ts`. Mounted by `differentials/differential-detail-page.tsx`, `services/service-detail-page.tsx`, `forms/form-detail-page.tsx`, `dsm/dsm-differential-considerations-page.tsx`, and — through a `"use client"` sibling module, because those pages are Server Components — `specifiers/specifier-nav-header.tsx`, `formulation/formulation-nav-header.tsx` and `dsm/dsm-diagnosis-nav-header.tsx`. Every declared section is pinned against rendered DOM by `tests/in-page-nav-route-sections.dom.test.tsx`.
+- **Shared secondary navigation**: `src/components/secondary-navigation.tsx` (`SecondaryNavigation`, route/action items, roving tablist) and `src/components/page-secondary-navigation.tsx` (`PageSecondaryNavigation`, mode destinations only). Mode destinations come from `src/lib/mode-secondary-navigation.ts` (`modeSecondaryNavigationRegistry`, no "Home" item). `GlobalSearchShell` renders it in normal flow at the top of `#main-content` for its owned namespaced modes; it self-suppresses on clean mode homes, on Therapy Compass, and on every information page — `hasLocalInformationPageNavigation` is now just `isInformationPage`, because each of those routes owns its own in-page navigation. The `section` kind and its "On this page" pill rail were removed once the last six routes moved onto `InPageNavHeader`; `route`/`action` survive as component API with tests but have no production constructor (`/issues #271`).
 - **Local filter fields** (sidebar "Search chats", document drawer "Find a document"/"Find a source PDF") are scoped filters, not global search; they share the `fieldControlWithIcon`/`fieldIcon` primitives.
 - **Wiring conventions** for buttons and route navigation (and the gates that enforce them — the dead-button ESLint rule and the orphan-route reachability test) live in `docs/wiring-conventions.md`.