ci: run unit tests on Linux; stabilize isToday test across time zones

Revert Unit tests to evoo-ci Linux for ffmpeg/libass coverage. Use a
previous-day instant that stays on the prior calendar date in UTC+14…UTC-12.

Co-authored-by: cynarAI <cynarAI@users.noreply.github.com>

.github/workflows/ci.yml

@@ -30,7 +30,8 @@ concurrency:
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 # Jobs that only need Node/pnpm/bash use [self-hosted, evoo-ci] so macOS runners (air, mini)
-# can share load. Linux-only work keeps the Linux label (Docker, xvfb, local Postgres :5433).
+# can share load. Linux-only work keeps the Linux label (Docker, xvfb, local Postgres :5433,
+# Homebrew ffmpeg with libass/subtitles filter for media unit tests).
 
 jobs:
   changes:
@@ -193,7 +194,7 @@ jobs:
     name: Unit tests
     needs: changes
     if: needs.changes.outputs.product == 'true'
-    runs-on: [self-hosted, evoo-ci]
+    runs-on: [self-hosted, evoo-ci, Linux]
     steps:
       - uses: actions/checkout@v5
         with:

apps/web/src/lib/heute-brief.test.ts

@@ -91,7 +91,8 @@ function run(overrides: Partial<RunActivityRow> = {}): RunActivityRow {
 describe("isToday", () => {
   it("matches same calendar day", () => {
     expect(isToday("2026-09-22T08:30:00.000Z", now)).toBe(true);
-    expect(isToday("2026-09-21T23:59:00.000Z", now)).toBe(false);
+    // Midday UTC on the previous day stays the previous calendar day in UTC+14…UTC-12.
+    expect(isToday("2026-09-21T12:00:00.000Z", now)).toBe(false);
   });
 });