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

Fixtures/README.md

@@ -4,13 +4,15 @@ Golden fixture boards for the storage-contract test suite — real on-disk folde
 
 Bundled into the unit-test target as a folder reference (see `project.yml`). Valid boards live under `Valid/`, fail-fast cases under `Malformed/`. Tests live in `KanbanTests/FixtureBoardTests.swift`.
 
+Hidden fixture files are named `.hidden-*` rather than `.DS_Store`: the repo's `.gitignore` ignores `.DS_Store` everywhere, so a fixture spelled that way would exist on the authoring machine and vanish from a fresh clone. The loader's rule is `.skipsHiddenFiles` — it is about the leading dot, not the name.
+
 Lane/card folder names are fixed literal lowercase-UUIDv4-shaped strings (never generated at test time), chosen so their lexicographic order matches the expected tie-break order — usually a leading digit (`10000000-...`, `20000000-...`, …) so folder order reads the same as array-index order in the tests. That is a fixture-authoring convention, not the loader's gate: the identity predicate is shape-only (`8-4-4-4-12` hex, **any case, any version** — 01-storage-format.md § Fractal layout ▸ Rules), and the case/version coverage lives in `KanbanTests/BoardLoaderTests.swift` rather than here.
 
 ## Valid/ — one board per tolerated/valid case
 
 | Board | Case |
 |---|---|
-| `rich-board.kanban` | A full-breadth well-formed board: 2 lanes, 3 cards, bodies, styling (background/icon/iconColor/width), unknown + reserved frontmatter keys, `attachments/` and `comments/` with real content. Also the board every `index.md` in the tree is round-tripped against. |
+| `rich-board.kanban` | A full-breadth well-formed board: 2 lanes, 3 cards, bodies, styling (background/icon/iconColor/width), unknown + reserved frontmatter keys, `attachments/` and `comments/` with real content. Its `attachments/` also carries all four listing shapes — two ordinary files, a hidden one, and a subfolder with a file — so `Card.attachments`' flat rule (01-storage-format.md § Attachments) is asserted against a real tree. Also the board every `index.md` in the tree is round-tripped against. |
 | `interrupted-create.kanban` | The motivating skip-not-error case: a UUID-shaped lane folder and a UUID-shaped card folder, each with no `index.md` yet (folder created, write not yet landed). |
 | `non-uuid-strays.kanban` | Non-UUID-shaped folders at both lane and card depth, with and without `index.md` — name shape gates candidacy before the file is ever read. |
 | `stray-files.kanban` | Stray (non-directory) files at board, lane, and card level — never level candidates, never warned about. |

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/attachments/.hidden-note.txt

@@ -0,0 +1 @@
+Hidden entries are never attachments (skipsHiddenFiles).

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/attachments/notes.txt

@@ -0,0 +1 @@
+Not a real .txt either — a stand-in attachment.

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/attachments/sub/nested.txt

@@ -0,0 +1 @@
+A subfolder file: tolerated, preserved, never surfaced.