Fix the 3am notification avalanche and the failing morning digest

Three bugs from the first day of real use.

1. Quiet hours were evaluated in UTC. The router is handed a UTC `now` and
   compared its hour against "22:00-07:00" directly, so notifications were
   silenced from 18:00 local -- prime reading time -- and the whole day's budget
   was released at 03:00 local. The reported avalanche landed at 03:39 and 03:55.
   Quiet hours are now converted to the reader's wall clock first.

2. The timezone never resolved anyway. TZ was "America/Louisville", which exists
   on this Arch host but NOT in a Debian container, which ships only the
   canonical "America/Kentucky/Louisville". The container fell back to UTC and
   `date` printed "America" as the zone abbreviation. The zone is now read from
   config rather than the environment, so a bad TZ cannot silently change
   behaviour, and the compose entry uses the canonical name. NOTE: ~20 other
   services in compose.yml carry the same bad string; they were left alone since
   it only affects their log timestamps.

3. Budgets are not a rate. Six notifications fired in a single minute because
   the daily allowance could all be spent in one cycle. Each lane now has a
   minimum gap (interest 75min, importance 30min) and sends at most one per
   cycle, which turns the budget into a rate spread across the day.

Separately, the morning digest had silently fallen back to the templated list.
The real 28-story payload takes 70.3s to generate against a 60s timeout. Raised
to 180s -- and write_prose now LOGS why it failed instead of returning None in
silence, which is what made a one-line timeout cost a debugging session.

pyproject.toml

@@ -12,6 +12,12 @@ dependencies = [
     "jinja2>=3.1",
     "uvicorn>=0.30",
     "python-multipart>=0.0.9",
+    "tomlkit>=0.13",
+    # Quiet hours and the digest hour are wall-clock decisions. System zoneinfo
+    # is normally present, but this makes the zone lookup independent of the
+    # base image -- Debian ships no America/Louisville, only the canonical
+    # America/Kentucky/Louisville.
+    "tzdata>=2024.1",
     "tomlkit>=0.15.1",
 ]