Build Preview mode rendering

The card body's resting state: swift-markdown (pinned 0.8.0, smart
typography off — Preview renders the bytes on disk) parsed into a pure
BodyMarkup model with UTF-8 source offsets, rendered on one hosted
TextKit 1 NSTextView — chosen because find-in-text is NSTextFinder,
checkbox clicks reuse AppKit character hit-testing, links are .link
attributes, and NSTextTable's automatic layout is exactly the
columns-sized-to-contents rule. The GFM subset renders per 05; HTML
stays verbatim code-styled text; relative images resolve against the
card folder while remote URLs are never fetched, drawing a quiet chip
instead. Task checkboxes are live: a click flips exactly one byte
through a fresh-read, refuse-uneditable, stamp, atomic-replace write —
the app's only offset-addressed write, so a moved target refuses as
staleTarget and what the user saw decides the direction, netting one
toggle on a double-click. Empty bodies open in Edit per CardBodyMode's
opening rule, applied once; the Edit surface itself stays an honest
read-only stub until its card. FindCommand prefers the card body's
find over board search when a card window is focused.

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

project.yml

@@ -10,6 +10,13 @@ packages:
   Yams:
     url: https://github.com/jpsim/Yams.git
     from: 6.0.0
+  # apple/swift-markdown — the card window's Preview parser (05-card-window.md ▸ Preview).
+  # Pinned to the next *minor* rather than the next major because the package is pre-1.0: a
+  # `from:` range here would silently accept 0.9's breaking changes, which is not what `from:`
+  # means for Yams at 6.x.
+  swift-markdown:
+    url: https://github.com/apple/swift-markdown.git
+    minorVersion: 0.8.0
 
 settings:
   base:
@@ -26,6 +33,8 @@ targets:
       - Kanban
     dependencies:
       - package: Yams
+      - package: swift-markdown
+        product: Markdown
     postBuildScripts:
       - script: '"${SRCROOT}/../indie-skills/skills/app-versioning/scripts/update_build_info.sh"'
         name: Update Build Info