ci(lint): a grown warning count names the file and line that grew it

lint:warnings failed with the total and the files holding the most of the rule, which are old ones the baseline allows; the file that tipped the count was never named, so finding it meant linting by hand. When a rule grows, the ratchet now lints the files that differ from the base twice, as they are and as they were there, and lists every one holding more of the rule, line and message. The base is TREK_LINT_BASE (the CI fetches the pushed-over commit on a push and the target branch on a pull request) or origin/dev; without it the report stays as it was.

.github/workflows/test.yml

@@ -257,6 +257,15 @@ jobs:
         # migration that changes a column regenerates it in the same change.
         run: cd server && npm run check:db-types
 
+      - name: Fetch the base the warnings are compared with
+        # lint:warnings names the file behind a grown count by linting it as
+        # it is on the base: the pushed-over commit on a push, the target
+        # branch on a pull request. A miss only drops that hint.
+        run: >-
+          git fetch --no-tags --depth=1 origin
+          "+${{ github.event_name == 'push' && github.event.before || format('refs/heads/{0}', github.base_ref || 'dev') }}:refs/remotes/lint-base"
+          || true
+
       - name: Lint
         # Errors fail, and the warnings per rule may not pass
         # scripts/eslint-baseline.json (src, tests and eslint-disable'd
@@ -264,6 +273,7 @@ jobs:
         # program, which outgrows Node's default ~4 GB heap on the runner.
         env:
           NODE_OPTIONS: --max-old-space-size=8192
+          TREK_LINT_BASE: refs/remotes/lint-base
         run: cd server && npm run lint:warnings
 
       - name: Formatting check
@@ -395,6 +405,15 @@ jobs:
         # one included, has to be clean (scripts/strict-lint.mjs).
         run: cd client && npm run lint:strict
 
+      - name: Fetch the base the warnings are compared with
+        # lint:warnings names the file behind a grown count by linting it as
+        # it is on the base: the pushed-over commit on a push, the target
+        # branch on a pull request. A miss only drops that hint.
+        run: >-
+          git fetch --no-tags --depth=1 origin
+          "+${{ github.event_name == 'push' && github.event.before || format('refs/heads/{0}', github.base_ref || 'dev') }}:refs/remotes/lint-base"
+          || true
+
       - name: Lint
         # Fails on any ESLint error, like lint:check did, and on any rule
         # whose warning count rises above scripts/eslint-baseline.json.
@@ -402,6 +421,7 @@ jobs:
         # whole TypeScript program, so it gets the heap the server lint gets.
         env:
           NODE_OPTIONS: --max-old-space-size=8192
+          TREK_LINT_BASE: refs/remotes/lint-base
         run: cd client && npm run lint:warnings
 
       - name: Page pattern check