Improve community call reminder: closed issues, doc link, Monday schedule

- Add closed issues from the last week (with issue author, not PR author)
- Add link to latest reductions.pdf documentation
- Move schedule from Tuesday to Monday (one day before the call)
- Topic date now shows tomorrow (the actual call date)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: GiggleLiu

.github/workflows/community-call.yml

@@ -2,8 +2,8 @@ name: Community Call Reminder
 
 on:
   schedule:
-    # Every Tuesday at 00:00 UTC = 08:00 HKT (2 hours before 10:00 HKT call)
-    - cron: '0 0 * * 2'
+    # Every Monday at 00:00 UTC = 08:00 HKT (one day before Tuesday 10:00 HKT call)
+    - cron: '0 0 * * 1'
   workflow_dispatch: # Manual trigger for testing
 
 jobs:
@@ -70,21 +70,44 @@ jobs:
             echo 'EOF'
           } >> "$GITHUB_OUTPUT"
 
+      - name: Collect closed issues from last week
+        id: closed
+        env:
+          GH_TOKEN: ${{ secrets.PROJECT_READ_TOKEN }}
+        run: |
+          SINCE=$(date -u -d '7 days ago' +%Y-%m-%dT%H:%M:%SZ)
+          ITEMS=$(gh issue list --repo "$GITHUB_REPOSITORY" --state closed \
+            --search "closed:>=$SINCE" --json number,title,url,author \
+            --jq '.[] | "- [#\(.number)](\(.url)) \(.title) (by @\(.author.login))"')
+
+          {
+            echo 'CLOSED<<EOF'
+            if [ -n "$ITEMS" ]; then
+              echo "**Closed this week:**"
+              echo "$ITEMS"
+              echo ""
+            fi
+            echo 'EOF'
+          } >> "$GITHUB_OUTPUT"
+
       - name: Post to Zulip
         env:
           ZULIP_BOT_EMAIL: ${{ secrets.ZULIP_BOT_EMAIL }}
           ZULIP_BOT_API_KEY: ${{ secrets.ZULIP_BOT_API_KEY }}
         run: |
-          TODAY=$(TZ=Asia/Hong_Kong date +%Y-%m-%d)
+          TOMORROW=$(TZ=Asia/Hong_Kong date -d '+1 day' +%Y-%m-%d)
           CALL_TIME="10:00 HKT (UTC+8)"
 
-          TOPIC="Community Call ${TODAY}"
+          TOPIC="Community Call ${TOMORROW}"
 
-          BODY="**Community Call — ${TODAY} at ${CALL_TIME}**
+          BODY="**Community Call — ${TOMORROW} at ${CALL_TIME}**
 
           **Join:** ${{ secrets.CALL_LINK }}
 
+          **Latest documentation:** [reductions.pdf](https://codingthrust.github.io/problem-reductions/reductions.pdf)
+
           ## Agenda
+          ${{ steps.closed.outputs.CLOSED }}
           ${{ steps.agenda.outputs.AGENDA }}
           **Open discussion** — bring your questions and ideas!