Build card faces with edge-accent styling

The card face becomes real: leading SF Symbol (card default doc.text,
tinted by a valid hand-written iconColor — schema yes, control no),
title or the quiet untitled placeholder, and a quiet paperclip when
the card has attachments — title-only by design, no body excerpt.
Color is the settled K1 edge accent, not a fill: background paints a
4pt stripe down the left edge, resolved through the ported pathfinder
palette (12 icon tints + 12 backgrounds carried over verbatim, plus
raw #RRGGBB[AA]); anything unresolvable paints nothing and stays on
disk exactly as written. The snapshot now carries each card's flat
attachment names — the loader's one read inside a card folder, shared
with the Writer's listing so the m5 carousel and m6 sidebar can never
disagree on order (Finder order, the Writer's existing comparator).
The face keeps its top-aligned structure so the sole-selection
carousel can expand inside the card without moving masonry neighbors.
18 new tests.

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

Kanban/Storage/BoardModel.swift

@@ -151,9 +151,11 @@ public struct Lane: Identifiable, Sendable, Equatable {
     public var isDeleted: Bool { !deleted.isMissing }
 }
 
-/// A card: `<root>/<guid>/<guid>/index.md`. Leaf of the fractal tree — `attachments/` and the
-/// (future, out-of-scope) `comments/` live alongside `index.md` on disk but are not modeled
-/// here.
+/// A card: `<root>/<guid>/<guid>/index.md`, plus the *names* of its attachments. Structurally
+/// still a leaf — `comments/` (future, out-of-scope) and the attachment files' contents live
+/// alongside `index.md` on disk and are not modeled here; `attachments` is the one thing the
+/// snapshot reaches inside a card folder for, because two board-window surfaces need it before
+/// any card window exists (see its own doc comment).
 public struct Card: Identifiable, Sendable, Equatable {
     public let id: ItemID
 
@@ -171,6 +173,25 @@ public struct Card: Identifiable, Sendable, Equatable {
     /// comment; the same reasoning applies here.
     public let order: Double
 
+    /// The card's attachment file names — **flat: top-level regular files only, in Finder
+    /// order** (01-storage-format.md § Attachments: "the app's attachment surfaces … are flat:
+    /// top-level files only", and "subfolders are tolerated, preserved verbatim, never created
+    /// by the app, and not surfaced"). Empty when the card has no `attachments/` folder, and
+    /// empty when it has one that couldn't be listed — the field is cosmetic, so a
+    /// directory-listing race degrades to "nothing to show" rather than failing a load.
+    ///
+    /// Names, not URLs: the two board-window consumers only need to know *whether*, *how many*,
+    /// and in *what order* — the face's quiet paperclip indicator (03-board-ui.md § Card face)
+    /// and the sole-selected card's attachment carousel. The card window's sidebar does its own
+    /// listing through `BoardWriter.listAttachments`, since it acts on the files rather than
+    /// showing them; that call answers through the very same enumeration
+    /// (`BoardLoader.attachmentNames(in:)`), so the two surfaces agree by construction.
+    ///
+    /// Freshness is the watcher's, by construction: it reloads on any change anywhere under the
+    /// board root, so an attachment added in Finder rebuilds the snapshot exactly like an edited
+    /// `index.md` does — no separate invalidation path to keep honest.
+    public let attachments: [String]
+
     /// The full parsed `index.md`; unknown/reserved keys ride along uninterpreted.
     public let document: FrontmatterDocument