a time slot naming no hour is asked about, never filled (V-579)

Both parsers answer a bare day word with that day at the current minute, so "на
завтра" set a reminder at 01:38, the minute he happened to be speaking. The gate
is textual now: NamesAnHour reads the sentence, and the slot stays empty when
nobody said an hour.

Beside it, NamesAnInterval and HourIsAmbiguous, which the owner's commit rule
reads. "на" joins "в" as a frame around a spoken hour in both parsers, a clock
keeps its meaning with a full stop after it, and the stub applies a day word and
a part-of-day qualifier from anywhere in the sentence rather than only from the
token after the hour.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/router/dateparser.go

@@ -54,7 +54,9 @@ try:
     # часов" is read as seven hours from now. Only a qualifier (already an
     # am/pm above) or a colon makes it read the hour, so give it the colon.
     # English "at 7" fails identically, so both prepositions are rewritten.
-    text = re.sub(r'(?<![\w:])(в|во|at)\s+([01]?\d|2[0-3])(?:\s+час(?:а|ов)?)?(?![\d:.\w])',
+    # "на 9" is the same hour said with the other preposition, and it was not
+    # read at all until V-579: "в 9" set the reminder and "на 9" did not.
+    text = re.sub(r'(?<![\w:])(в|во|на|at)\s+([01]?\d|2[0-3])(?:\s+час(?:а|ов)?)?(?![\d:.\w])',
                   lambda m: '%s %02d:00' % (m.group(1), int(m.group(2))), text, flags=re.IGNORECASE)
     settings = {'PREFER_DATES_FROM': 'future', 'RELATIVE_BASE': now}
     # Two-step: search_dates finds the date substring in text,