feat: make calendar import timezone-correct and bounded (Closes #1212)

tests/e2e/test_mobile_week_ahead_release.py

@@ -30,7 +30,7 @@ def test_release_artifact_plans_seven_touch_safe_mobile_dates(
     try:
         with release_server(archives[0], tmp_path, f"http://127.0.0.1:{fake.server_port}") as origin, sync_playwright() as playwright:
             browser = playwright.chromium.launch(args=["--ignore-certificate-errors"])
-            page = browser.new_page(viewport={"width": width, "height": height})
+            page = browser.new_page(viewport={"width": width, "height": height}, timezone_id="UTC")
             page_errors: list[str] = []
             page.on("pageerror", lambda error: page_errors.append(str(error)))
 
@@ -107,9 +107,10 @@ def test_release_artifact_plans_seven_touch_safe_mobile_dates(
             added = (date.today() + timedelta(days=4)).strftime("%Y%m%d")
             calendar = (
                 "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nBEGIN:VEVENT\r\n"
-                f"SUMMARY:{private_title}\r\nDTSTART:{tomorrow}T090000\r\n"
-                f"DTEND:{tomorrow}T100000\r\nRRULE:FREQ=DAILY;COUNT=3\r\n"
-                f"EXDATE:{excluded}T090000\r\nRDATE:{added}T090000\r\nEND:VEVENT\r\nEND:VCALENDAR"
+                f"SUMMARY:{private_title}\r\nDTSTART;TZID=America/New_York:{tomorrow}T050000\r\n"
+                f"DTEND;TZID=America/New_York:{tomorrow}T060000\r\nRRULE:FREQ=DAILY;COUNT=3\r\n"
+                f"EXDATE;TZID=America/New_York:{excluded}T050000\r\n"
+                f"RDATE;TZID=America/New_York:{added}T050000\r\nEND:VEVENT\r\nEND:VCALENDAR"
             )
             unsupported_title = "Private monthly board review"
             unsupported_calendar = (