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

KanbanTests/SymbolPickerTests.swift

@@ -98,7 +98,9 @@ struct SymbolPickerFullCatalogTests {
 
     @Test("A nonexistent bundle path falls back to the merged curated set, sorted and unique")
     func nonexistentPathFallsBack() {
-        let expected = Set(SymbolPickerCatalog.defaultSet + CuratedSymbols.all).sorted()
+        // `CuratedSymbols.all` was one flat list; 2026-08-09 split it into three level-specific sets
+        // plus `combined`, the union this fallback still reads (`SymbolPicker.swift`'s `load`).
+        let expected = Set(SymbolPickerCatalog.defaultSet + CuratedSymbols.combined).sorted()
         #expect(SymbolPickerCatalog.fullCatalog(bundlePath: "/nonexistent") == expected)
     }
 }