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

KanbanTests/FixtureBoardTests.swift

@@ -117,6 +117,38 @@ struct FixtureRichBoardTests {
         #expect(done.cards[0].title.value == "Ship v1")
     }
 
+    /// `attachments/` is **flat** (01-storage-format.md § Attachments): the card's listing is its
+    /// top-level regular files and nothing else. This card's folder holds all four shapes on real
+    /// disk — two ordinary files, a hidden one, and a subfolder with a file in it — so the rule is
+    /// asserted against a filesystem rather than against a mock.
+    ///
+    /// The excluded three are excluded for three different reasons and only one of them is stated
+    /// in the design doc: subfolders are "tolerated, preserved verbatim … and not surfaced"; the
+    /// hidden file is the loader's uniform `.skipsHiddenFiles` stance (a `.DS_Store` is not
+    /// anyone's attachment); symlinks are the loader's never-resolve stance, covered in
+    /// `BoardLoaderTests` because git cannot carry that shape into a fixture reliably.
+    @Test func aCardListsOnlyTheTopLevelFilesOfItsAttachmentsFolder() throws {
+        let result = try loadFixture("Valid/rich-board.kanban")
+        let doing = try #require(result.model.lanes.first { $0.id.rawValue == RichBoard.laneDoing })
+        let taxonomy = try #require(doing.cards.first { $0.id.rawValue == RichBoard.cardTaxonomy })
+
+        #expect(taxonomy.attachments == ["notes.txt", "sketch.png"])
+    }
+
+    /// The overwhelmingly common shape: no `attachments/` folder at all. It reads as an empty
+    /// listing, never as a warning or a failure — nothing has been attached yet is an ordinary
+    /// state, and it is what makes the face's paperclip indicator absent by default.
+    @Test func cardsWithoutAnAttachmentsFolderListNothing() throws {
+        let result = try loadFixture("Valid/rich-board.kanban")
+        let doing = try #require(result.model.lanes.first { $0.id.rawValue == RichBoard.laneDoing })
+        let second = try #require(doing.cards.first { $0.id.rawValue == RichBoard.cardSecond })
+        let done = try #require(result.model.lanes.first { $0.id.rawValue == RichBoard.laneDone })
+
+        #expect(second.attachments.isEmpty)
+        #expect(done.cards.map(\.attachments) == [[]])
+        #expect(result.warnings.isEmpty)
+    }
+
     @Test func boardUnknownAndReservedKeysPreserveOrder() throws {
         let result = try loadFixture("Valid/rich-board.kanban")
         // schema-owned keys (schema, title, created, modified, modified-by, background, icon,