Move the to-do list from NOTES.md to a kandown board

Each note is a task in tasks/ with the owner's words under ## Context; the
board rules are in .kandown/kandown_work.md and docs/kandown.md explains how
kandown works here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.kandown/.gitignore

@@ -0,0 +1,9 @@
+daemon.json
+daemon.lock
+.undo/
+
+# Local extension state. Which extensions you enabled and which you trusted is a
+# per-machine decision, and a committed copy is ignored at load time anyway
+# (see docs/EXTENSIONS.md).
+extensions/enabled.json
+extensions/trust.json