meeting words come from the units table; the constants are now defaults

MEETING_DAY, MEETING_DAYS, MEETING_DAY_ABBR, PACK_TIME, TROOP_TIME,
PACK_CLOCK and TROOP_CLOCK were the last thing a leader could not change
without a commit. identity.meeting_words() derives all seven from the units
rows; app.py refreshes the module globals from it on a 30-second TTL in a
middleware, and the page templates - f-strings that read those globals when a
route runs - are untouched. A row that cannot supply a word keeps the
default, so a half-filled unit degrades to today's copy rather than a blank.

The day words come from the pack row: the site's copy assumes both units
meet the same night, and if that changes the copy needs rewriting, not a
bigger constant. Proven on a throwaway container with a DB copy: patching
pack73 to Thursday 18:15 changed the homepage, cubs, troop and meta
description; patching back restored them. tests/smoke_identity.py 59 -> 66.

app/identity.py

@@ -338,6 +338,43 @@ def get_unit(slug_or_id):
 # code change.
 UNIT_MEETS_FIELDS = ("meets_weekday", "meets_time", "meets_at")
 
+WEEKDAY_NAMES = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
+
+
+def clock_words(hhmm):
+    """"18:00" -> ("6:00 PM", "6:00"). Returns None on anything unparseable so
+    the caller keeps its fallback rather than rendering a blank."""
+    try:
+        t = datetime.datetime.strptime(str(hhmm), "%H:%M")
+    except (TypeError, ValueError):
+        return None
+    h12 = t.hour % 12 or 12
+    clock = "%d:%02d" % (h12, t.minute)
+    return ("%s %s" % (clock, "AM" if t.hour < 12 else "PM"), clock)
+
+
+def meeting_words(units, defaults):
+    """The seven seasonal strings app.py renders, derived from the units rows.
+
+    `defaults` is the dict of the code constants; any word a row cannot supply
+    keeps its default, so a half-filled unit row degrades to today's copy and
+    never to a blank page. The day words come from the PACK row: the site's
+    copy assumes both units meet the same night ("right after the pack"), and
+    if that ever changes the copy needs rewriting, not a bigger constant.
+    """
+    out = dict(defaults)
+    by = {u.get("slug"): u for u in units}
+    pack, troop = by.get("pack73"), by.get("troop73")
+    day = (pack or troop or {}).get("meets_weekday")
+    if isinstance(day, int) and 1 <= day <= 7:
+        name = WEEKDAY_NAMES[day - 1]
+        out["MEETING_DAY"], out["MEETING_DAYS"], out["MEETING_DAY_ABBR"] = name, name + "s", name[:3]
+    for row, tkey, ckey in ((pack, "PACK_TIME", "PACK_CLOCK"), (troop, "TROOP_TIME", "TROOP_CLOCK")):
+        w = clock_words((row or {}).get("meets_time"))
+        if w:
+            out[tkey], out[ckey] = w
+    return out
+
 
 def update_unit_meets(slug_or_id, fields):
     """Change when and where a unit meets.