feat(ui): shared migration primitives (UI migration PR 3) (#1122)

* feat(ui): shared migration primitives (UI migration PR 3)

The component kit every page migration (PR 4-8) builds on:

- ContextPicker: the one-per-page chip-dropdown context scope (convention
  8), right-aligned popover with checks and muted annotations
- FyPicker: fiscal-year picker on ContextPicker with the same controlled
  API and per-company localStorage key as FiscalYearSelector, which it
  replaces page by page from PR 4
- SplitButton: primary + caret menu, last-used mode persisted per user
  via ui_state.create_mode (lib/ui-state/client, unit-tested); nav
  persistence refactored onto the same helper
- ConfirmDialog: centered min-460px confirm-up-front dialog (convention
  10) with pending state on an awaitable onConfirm
- HelpPopover: 17px "?" after the H1 opening an anchored popover
  (convention 7); PageHeader gets a `help` slot
- AttnLine: the one-ochre-sentence attention pattern (convention 6) with
  optional inline action; new AA-safe --attn token pair
- RowStatus: chips-mark-exceptions helper (convention 5)
- SlideOver: right review panel, 480px, 18px inset, rounded, veil + Esc
  (convention 13), with header kicker / body / footer slots
- Stagger: .stagger-enter applied to the five target pages' list
  containers (bookkeeping, transactions, pending, invoices,
  supplier-invoices); structural loading.tsx added for supplier-invoices,
  customers, kpi, pending, deadlines

No page adopts the new pickers/dialogs yet: that is PR 4-8, one page per
PR against this kit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(ui): FyPicker chip must not double the Rakenskapsar label

Real fiscal periods are often named "Rakenskapsar 2026" already; only
prefix the label when the period name lacks it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

DECISIONS.md

@@ -338,3 +338,4 @@ One line per decision: `[YYYY-MM-DD] <decision>: <why>`. Appended by agents and
 [2026-07-23] UI-migration plan authored (dev_docs/ui_migration_plan.md): shell-first sequence (tokens/nav/primitives) then Bokforing/Transaktioner/Granskning/Kund+Lev-fakturor; concept artifact is the reference; 14 locked design conventions codified: chose PR-per-page over big-bang to keep founder visual sign-off per merge.
 [2026-07-23] Frame layout (UI-migration PR 1) is md:-gated and the panel owns desktop scroll: mobile keeps document flow + bottom nav (concept is desktop-first), and since Next's window scroll-to-top never fires for an inner scroll container, MainContainer resets panel scroll on route change. Button default size drops fixed h-10 for natural pill height (7px/16px padding per locked convention 3); sm/lg/icon keep their heights.
 [2026-07-23] Nav PR 2: ui_state persisted as one jsonb bag on user_preferences (founder-approved migration 20260723120000) rather than per-preference columns: cosmetic, never load-bearing, grows with PR 3/4 split-button modes. Sidebar width driven by an inline --nav-w CSS variable on #dash-shell instead of a [data-nav-collapsed] attribute rule: the Tailwind 4/Lightning CSS pipeline silently dropped the top-level attribute-selector rule from compiled output, and the inline variable is pipeline-proof. Register/Bokslut folds default closed (concept tidiness), forced open by an active child route. Discord-community row skipped: no invite URL exists in the repo; add when one lands.
+[2026-07-23] PR 3 primitives: new --attn token pair (38 50% 34% light / 38 45% 62% dark) for the one-sentence AttnLine instead of reusing --warning: the warning tone fails WCAG AA as 12.5px body text on the page background; chips/charts keep --warning. Stagger applied via className on the five target pages' DataList/TableBody containers (plan item 7), not baked into the DataList primitive: remaining pages adopt it in their own migration PRs where their skeletons are aligned at the same time.