fix(ui): own the time picker so it follows the 24-hour preference

The native datetime-local / time picker renders its clock and AM/PM
toggle by the browser UI language, not the page lang or the app's
time-format preference — so an English-language browser showed AM/PM
even with 24-hour selected. Replace the native time control with an
app-controlled TimeField (text entry + a dependency-free popover of
hour/minute, plus AM/PM in 12-hour mode) whose hour cycle always tracks
the preference. DateTimeField now composes the native calendar (date)
with TimeField (time); the committed value stays a local
yyyy-MM-ddTHH:mm string, and min/max clamp the recombined value.

Also thread the time-format preference into the doctor-report PDF so its
generated-at timestamp honours it instead of the locale default.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.25.3
+  version: 1.25.4
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.