feat(viewer): MSK datetime + done-cutoff expander [v0.3.0]

Closes 2 more UX-round1 fixes (5/6 done; task-numbers remains
design-first cross-repo, awaiting user decision).

ux-full-datetime: formatMskDateTime(iso) → "YYYY-MM-DD HH:MM МСК".
UTC+3 fixed (no-DST since 2011). Tooltip retains full ISO for
copy-paste. Relative age stays in card-meta. Mirrored in board.js
renderCard re-render path.

ux-done-cutoff: source unchanged (render-side cutoff). Done column
sorts by last_commit_iso desc, first 10 visible, rest get
data-overflow="true" (CSS hides). Column bottom gets
"show N more" expander; click toggles col.show-overflow class +
button text "collapse". Non-done columns untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "board-viewer",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "private": true,
   "type": "module",
   "description": "Read-only HTML kanban viewer over Gitea API",