replace symbol grid in card window sidebar with a compact symbol picker

The card window sidebar's Style section embedded StyleEditorView symbols-only
(showsBackground: false, showsSymbols: true), drawing the curated grid whole
inside the sidebar's own scroll view — a permanently open 5-7 row grid ahead
of every other section. Replace it with the reusable compact SymbolPicker
(already used by BoardInfoPopover for the board's glyph): a single well at
rest, the grid only inside its own popover.

- CardStyleSection no longer instantiates StyleEditorView at all. A new
  "Symbol" row mirrors the existing "Background" row's inspector shape
  (caption leading, control trailing), wiring SymbolPicker's onSelect/
  onSelectColor to icon/iconColor through StyleCommand.apply(...on: undo),
  the exact funnel the background combo already rides — so the card window's
  undo session semantics (13-native-undo.md) are unchanged.
- The picker is fed CuratedSymbols.available rather than its own smaller
  general-purpose default, so a card's curated vocabulary doesn't shrink.
- StyleEditorLayout.sidebar and showsBackground stay in StyleEditor.swift
  (still correct, still tested) rather than being cut as dead code — a
  separate, larger cleanup this card doesn't make (recorded on the card).
- DESIGN/03-board-ui.md and DESIGN/05-card-window.md: updated the sentences
  describing the sidebar hosting the style editor's symbol grid to describe
  the compact picker instead.
- Tests: CardSessionUndoTests gains a symbol/tint analogue of the existing
  background-combo session-routing test; CardSidebarTests gains a curated-set
  tripwire and an updated file-header note.

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

DESIGN/03-board-ui.md

@@ -41,7 +41,7 @@ Toolbars are **pure enhancement**: every function they host already has a menu i
 
 ### Controls (settled)
 
-One **style editor** component — a background palette grid and a curated symbol grid — presented from two anchors: **embedded** in the card window sidebar's Style section (05-card-window.md), and as a **popover** opened by Style… from a card/lane context menu or the menu bar (Board ▸ Style…, ⌥⌘S — 11-command-nexus.md; selection-aware: it styles the selected cards or lane, and with nothing selected, the board). One component, one behavior — replacing the pathfinder's swatch-row-plus-Style-popover split, whose functions were right and whose form wasn't. **The anchors compose the halves they need** (2026-08-06): the card sidebar shows the symbol grid with the **color combo** (below) standing in for the background half — the narrow context the combo was built for; the Style… popover carries both grids in full. (The board popover was briefly a third anchor — the background half embedded in its Theme tab — until the 2026-08-07 Theme rework made that tab preset-only; Style… with nothing selected is the board's manual grid now, and the popover's symbol picker beside the rename field still owns the board glyph.)
+One **style editor** component — a background palette grid and a curated symbol grid — presented as a **popover** opened by Style… from a card/lane context menu or the menu bar (Board ▸ Style…, ⌥⌘S — 11-command-nexus.md; selection-aware: it styles the selected cards or lane, and with nothing selected, the board). One component, one behavior — replacing the pathfinder's swatch-row-plus-Style-popover split, whose functions were right and whose form wasn't. **The card window sidebar now styles through the compact `SymbolPicker` instead of this component** (2026-08-06 anchor-ownership rule for the background half; the symbol half followed the same way on 2026-08-08): the sidebar pairs the **color combo** (below) — standing in for the background half, the narrow context the combo was built for — with the picker's own well and popover-hosted `CuratedSymbols` grid, so this component now has exactly one anchor left, the Style… popover, which alone carries both grids in full. (The board popover was briefly a third anchor — the background half embedded in its Theme tab — until the 2026-08-07 Theme rework made that tab preset-only; Style… with nothing selected is the board's manual grid now, and the popover's symbol picker beside the rename field still owns the board glyph — the same `SymbolPicker` the card sidebar now uses.)
 
 - **Curated-first, panel-backed** (re-ratified 2026-08-06, reversing 2026-07-29's palette-only ruling): the background grid offers the 12 palette colors — every one AA-verified through one code path (ratified 2026-07-29: palette names route through the same runtime ink-selection seam as hand-written hex — the appearance flip picks the readable label vocabulary — and PaletteContrastTests pins that the chosen ink meets AA in both appearances for all 12 backgrounds, so palette drift can never silently break it) — plus a leading **None** well that removes the `background` key. Beside the grid the vocabulary now has a second, compact form: the **color combo** — a swatch-faced popup listing None, the role's twelve, the current off-palette value verbatim when there is one, and **Other…**, which opens the system Colors panel. The panel is the in-app escape hatch the 2026-07-29 ruling withheld: a pick landing exactly on a palette color stores the *name* (so a re-pick never drifts to a hex spelling), anything else stores the hex — the same unlimited vocabulary hand-editing always had, now pickable. An arbitrary pick changes no contrast story (it lands on the identical runtime ink computation hand-written hex already gets — 10-accessibility.md), and the quick-style recents stay palette-vocabulary: a panel pick never enters them.
 - **Curated symbol grid**: a hand-picked set (roughly five dozen kanban-relevant SF Symbols); its leading well is the level's default symbol and removes the `icon` key. Any other SF Symbol name works written by hand — named symbols the running OS knows, that is: inventories grow per macOS release, so a newer-OS name renders the level default on an older Mac, value preserved on disk — the palette stance again. No full-browser escape hatch in-app; the raw file is the escape hatch. (Symbols keep this stance deliberately — the 2026-08-06 color-panel reversal above is colors only: the system offers a Colors panel worth deferring to, and no symbol browser of equal standing.)