Three curated symbol vocabularies — boards, lanes, and cards each pick from their own shelf

`CuratedSymbols` was one flat ~65-glyph list serving every style-editor target alike. It is
now three level-specific sets — `boards` (project/container/identity), `lanes`
(workflow/stage/status), `cards` (work-item/content) — each ~30-40 entries, seeded from the
original list and `SymbolPickerCatalog.defaultSet`, reorganized by which level a glyph actually
reads as being about. Overlap is kept where a glyph genuinely fits everywhere (`flag`, `star`).

Wiring:
- `BoardInfoPopover`'s board-glyph `SymbolPicker` now passes `CuratedSymbols.availableBoards`
  instead of the picker's domain-agnostic default.
- The card sidebar's `SymbolPicker` (`CardSidebarSections`) now passes
  `CuratedSymbols.availableCards` instead of the old flat `available`.
- The style editor's own curated grid (`StyleEditorView`, the Style… popover's only remaining
  anchor) reads `CuratedSymbols.availableForStyleEditor(level:spansLevels:)`: a homogeneous
  target reads its own level's set, and a target that somehow spans more than one level (today
  unreachable — 04-interactions.md's cards-XOR-lanes rule keeps a live selection homogeneous)
  reads the three combined, via a new `BoardStore.styleTargetSpansLevels` seam that asks the
  question `styleLevel(of:)` deliberately collapses.
- `CuratedSymbols.combined` (the three sets' stable-order union) also replaces the old `.all`
  in `SymbolPickerCatalog`'s full-catalog fallback.
- `SymbolPickerCatalog.defaultSet` is kept as the fallback for a caller naming no level (a
  future saved-search picker, say) rather than retired.

DESIGN/03-board-ui.md and DESIGN/05-card-window.md's Styling/sidebar prose amended minimally
where they named "the curated set" as a single list.

Tests: three new/rewritten suites in KanbanTests/StyleModelTests.swift (set shape, availability,
overlap, `combined`, the style-editor level/span decision, the board-anchor width tripwire), one
new test in KanbanTests/StyleWriteTests.swift (`styleTargetSpansLevels`), and the old
single-list-pinning tests in KanbanTests/SymbolPickerTests.swift and KanbanTests/CardSidebarTests.swift
updated to the new set names. 2834 tests, 487 suites green (KanbanTests, arm64); one unrelated
flaky failure (RootRecoveryTests.vanishAndReturn under full-suite load) passed clean in isolation.

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

Kanban/UI/Board/BoardInfoPopover.swift

@@ -318,6 +318,11 @@ struct BoardInfoView: View {
                     SymbolPicker(
                         current: store.snapshot.icon.value,
                         fallback: ItemSymbol.board,
+                        // Board-level: project/container/identity-flavored, not the picker's
+                        // domain-agnostic default (`CuratedSymbols`' three-set split, 2026-08-09) —
+                        // this well is the board's own glyph, so it reaches for the same vocabulary
+                        // the style editor's grid would offer a board target.
+                        symbols: CuratedSymbols.availableBoards,
                         onSelect: { name in
                             StyleCommand.apply(
                                 icon: name.map { StyleChange.set($0) } ?? .remove,