## Summary
- Split the header into two zones: a **logo zone** whose width tracks the sidebar (16 rem expanded / 4 rem collapsed), and the existing search + actions cluster on the right.
- The logo glyph stays at both widths; the "APF Portal" wordmark hides when the rail collapses, mirroring the sidebar's icon-only mode.
- Promote the sidebar's `collapsed` state to a new [`LayoutStateService`](apps/portal-shell/src/app/state/layout-state.service.ts) (Signals + `localStorage`) so header and sidebar share a single source of truth.
## Why a service rather than prop-drilling
Two reasons:
1. The state is **shell-level**, not sidebar-internal — the header now reads it, and future surfaces (right rail, breadcrumbs, command palette) will too. Passing it down via inputs would force `<app-root>` to act as the owner and turn every intermediate component into a relay.
2. As we add other cross-cutting shell state (density, theme, panel pinning, RTL), they all belong in the same place. `LayoutStateService` is the natural collector and stays trivial as long as we don't over-broaden it. v1 ships with one signal — keeping it narrow.
The service is `providedIn: 'root'` (singleton), Signals-only, and owns localStorage persistence — same UX as before, just relocated.
## Decisions worth flagging
- **Widths stay duplicated between `header.scss` and `sidebar.scss`** (16 rem / 4 rem). Extracting a shared SCSS variable would be premature — only two callers, and the coupling is loud (cross-file comment in `header.scss`). If a third surface needs the same widths, we promote to a shared token.
- **Border continuity.** The logo zone's right border and the sidebar's right border share the same x coordinate, so they read as one continuous vertical separator running the full shell height. Same `#e5e7eb` so the seam is invisible.
- **Width transition** matches the sidebar's (`0.18s ease-out`) and is skipped under `prefers-reduced-motion: reduce`.
- **Sidebar component lost its private state.** Its own signal + effect + storage glue is gone; it delegates reads to the service and the toggle click to `layout.toggleSidebar()`. Net `sidebar.ts` shrunk by ~15 lines.
## Test plan
- [x] `pnpm exec nx run-many -t lint test build --projects=portal-shell` — green (25 / 25 specs, +6 for the new service spec + header zone tests).
- [x] Production build under bundle budgets (100 kB gzip initial — +0.2 kB vs main).
- [ ] Manual: load `/`, confirm the logo zone's right edge aligns exactly with the sidebar's right edge at both widths.
- [ ] Manual: toggle the sidebar → both columns animate in sync; wordmark hides; logo glyph stays centered in the 4 rem zone.
- [ ] Manual: reload after toggling → both header and sidebar restore to the persisted state.
- [ ] Manual: `prefers-reduced-motion: reduce` → no width animation in either zone.
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Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #85
julien
b6aa17f6a0