test(e2e): deselect by clicking a corner away from the shape

The test clicked the canvas at (10, 10) to deselect. When the click on the
shape before it needed retries, Playwright scrolled the shape into the
container's top-left corner, so the next click landed on the shape and the
selection stayed (seen on the main run of cd5352c and on #973). The new
clickEmptyCanvas helper clicks the corner farthest from the shape.
Reproduced locally by scrolling the shape into the corner: the old click
keeps the selection, the helper clears it.

.github/workflows/wait-for-confirmation.yml

@@ -1,55 +0,0 @@
-# Issues labelled "wait for confrim" are waiting for the reporter. After 15
-# days without activity the issue gets a reminder and the "no response"
-# label; after 15 more days it is closed. A reply from the reporter removes
-# both labels, so the issue shows up as needing the maintainer again.
-name: Wait for confirmation
-
-on:
-  schedule:
-    - cron: "17 3 * * *"
-  workflow_dispatch:
-  issue_comment:
-    types: [created]
-
-permissions:
-  issues: write
-
-jobs:
-  remind-and-close:
-    if: github.event_name != 'issue_comment'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/stale@v9
-        with:
-          only-issue-labels: "wait for confrim"
-          days-before-issue-stale: 15
-          days-before-issue-close: 15
-          days-before-pr-stale: -1
-          days-before-pr-close: -1
-          stale-issue-label: "no response"
-          stale-issue-message: >-
-            Still there? We asked for more information 15 days ago. A reply
-            would help; if we hear nothing in another 15 days this issue will
-            be closed. It can be reopened any time.
-          close-issue-message: >-
-            No reply in 30 days, so this issue is closed for now. If the
-            problem is still there, reply or reopen it.
-          close-issue-reason: not_planned
-          remove-stale-when-updated: true
-
-  reporter-replied:
-    if: >-
-      github.event_name == 'issue_comment' &&
-      contains(github.event.issue.labels.*.name, 'wait for confrim') &&
-      github.event.comment.user.type != 'Bot' &&
-      !contains(fromJSON('["OWNER","MEMBER","COLLABORATOR"]'), github.event.comment.author_association)
-    runs-on: ubuntu-latest
-    steps:
-      - name: The reporter answered, so the issue is the maintainer's again
-        run: >-
-          gh issue edit "$NUMBER" --repo "$REPO"
-          --remove-label "wait for confrim" --remove-label "no response"
-        env:
-          GH_TOKEN: ${{ github.token }}
-          NUMBER: ${{ github.event.issue.number }}
-          REPO: ${{ github.repository }}