Build the styling system and shared style editor

One style-editor component, anchor-agnostic: a background grid (None
well plus the 12 palette colors) and a curated symbol grid (the
pathfinder's five-dozen set, leading well removing the icon key for
the level default), selection-aware across cards, lanes, and the
board itself. Batch edits compute per-dimension state — uniform,
mixed (no well selected), or an off-palette value labeled verbatim
outside the grids — and choosing a well applies to the whole target
set as one write bracket, skipping no-ops per field. The popover
tracks its target set live per the freshly ratified rule: targets
re-resolve by UUID on every reload, a vanished target leaves the set,
an emptied set dismisses the editor, and nothing ever silently
retargets to the board. Anchors landing now: Board > Style
(Opt-Cmd-S) and the card/lane context menus, which also carry the
quick-style recents row (app-wide, persisted, capped at six, None
never recorded) and the lane's width control twinning the menu
chords. The styling system's other two renders arrive with it: a
lane's background paints the C7 top-edge band, the board's paints
the window content background — malformed values paint nothing and
stay byte-identical on disk. 31 new tests.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/UI/Palette.swift

@@ -63,9 +63,46 @@ enum Palette {
 }
 
 // The pathfinder's panel round-trip helpers (`NSColor.paletteHexString`, `Palette.name(forHex:)`)
-// and its swatch drawing are deliberately not ported yet: nothing writes a colour until the style
-// editor lands, and an unused writer is a claim about a surface that doesn't exist. The styling
-// card brings them back when the editor needs them.
+// stay unported: they exist to turn a colour the *system picker* returned back into a palette name,
+// and this app has no colour picker — "custom hex is not pickable in-app" (03 § Styling ▸ Controls)
+// makes the whole round trip a surface that doesn't exist. Its swatch drawing, on the other hand, is
+// below: a menu can only render `Image`/`Text`, so the quick-style row's dots have to be pictures.
+
+// MARK: - Menu swatches
+
+/// A colour value drawn as a picture, for the one surface that cannot take a SwiftUI shape: **menu
+/// items**. AppKit renders a menu row from its label's image and text, so the quick-style recents row
+/// (03-board-ui.md § Styling ▸ Controls) needs an `NSImage` per dot where the editor's own wells are
+/// ordinary views.
+enum PaletteSwatch {
+
+    /// A filled dot for `value` (a palette name or `#RRGGBB[AA]` hex), hairline-bordered.
+    ///
+    /// The border is not decoration: the background palette contains `chalk` (`#FFFFFF`), and an
+    /// unbordered white dot on a light menu is an invisible menu item — the same reason the editor's
+    /// wells are stroked (10-accessibility.md's contrast stance applied to the app's own chrome).
+    ///
+    /// A value that resolves to nothing draws the border alone rather than a guessed colour, matching
+    /// every other lenient rendering here: there is no colour, so show none.
+    static func circleImage(for value: String, diameter: CGFloat = 14) -> NSImage {
+        let color = Palette.nsColor(for: value)
+        return NSImage(size: NSSize(width: diameter, height: diameter), flipped: false) { rect in
+            let inset = rect.insetBy(dx: 0.5, dy: 0.5)
+            let path = NSBezierPath(ovalIn: inset)
+            // Under a translucent colour the menu's own backdrop would show through unevenly across
+            // appearances; filling the standard control backdrop first makes the dot composite the
+            // same way in light and dark. An opaque colour covers it completely.
+            NSColor.textBackgroundColor.setFill()
+            path.fill()
+            color?.setFill()
+            path.fill()
+            NSColor.separatorColor.setStroke()
+            path.lineWidth = 1
+            path.stroke()
+            return true
+        }
+    }
+}
 
 extension Palette {