fix(epic-execute): make --skip-done case-insensitive for status matching

The script marks stories with lowercase "done" but was checking for
capitalized "Done", causing --skip-done to never match completed stories.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/epic-execute.sh

@@ -1819,9 +1819,9 @@ for story_file in "${STORIES[@]}"; do
         fi
     fi
 
-    # --skip-done: Skip stories with Status: Done
+    # --skip-done: Skip stories with Status: done (case-insensitive)
     if [ "$SKIP_DONE" = true ]; then
-        if grep -q "^Status:.*Done" "$story_file" 2>/dev/null; then
+        if grep -qi "^Status:.*done" "$story_file" 2>/dev/null; then
             log_warn "Skipping $story_id (Status: Done)"
             ((SKIPPED++))
             update_story_metrics "skipped"