feat: a calendar of the rules the page states, and a list of the rest

[ChelseaKR]

What was missing

Downstream tools that compute over a time-of-use schedule need machine-checkable
time rules. The parser reads them and emits them as prose plus, where the
document states a bare range, a start and an end.

This is the first consumer-facing derivation the project ships, which makes
the fence more important than the feature: a calendar that quietly omits the
windows it could not express looks like a complete calendar.

What changed

ca-tariff-parse calendar tests/golden/smud-r-tod.json --dir dist/calendar

writes smud-r-tod.ics and smud-r-tod.refused.json — both, always. A
missing refusal file reads as "no refusals"; an empty list reads as "nothing was
refused". Those are different statements and only one of them is a measurement.

A VEVENT is written only where it re-expresses text the parser already
committed to. Everything else is refused, with the reason, the citation and the
verbatim text it refused:

• a residual window is refused because the parser already refused to give it
  hours, and deriving them here would undo that refusal;
• a window defined by exception ("Weekdays between noon and midnight except
  during the Peak hours") is refused — the exception is prose this module cannot
  subtract;
• a window with hours but no stated day type is refused rather than assumed
  daily;
• a window whose end is at or before its start crosses midnight, and
  splitting it is a decision the document did not make;
• a holiday day_rule outside a closed grammar (fixed day, ordinal weekday,
  last weekday) is refused. Day after Thanksgiving is a real rule with a
  defensible date and it is not in the grammar, so it is refused rather than
  rendered as the fourth Friday. A guess in a calendar entry has a calendar
  entry's authority.

Season bounds only where the season names whole months. BYMONTH selects
whole months and nothing else, so Summer (Jun 1 - Sept 30) becomes
BYMONTH=6,7,8,9, while Jun 15 - Sept 30 would have to be widened or narrowed
and is left unbounded and marked X-CA-SEASON-BOUNDS:partial.

No time zone is inferred, and the file says so. Recurrences are anchored to
1970 because a published rule states no year; the file says only the month, day
and time of a DTSTART mean anything, and every DTSTART is a real instance of
its own rule so a reader cannot treat it as an extra occurrence.

Nothing reads the clock. DTSTAMP is the document's own retrieval date, or
the epoch when it states none — a generation time would make two renderings of
one parse differ.

A watch baseline is refused outright: it omits the verbatim prose, and a refusal
that cannot quote what it refused is not one.

On the real documents

document	windows rendered	holidays rendered	refused
smud-r-tod	2 of 5	11 of 11	3
smud-ci-tod1	0 of 5	11 of 11	5
smud-r, smud-ssr	0 of 0	0 of 0	0

smud-ci-tod1 states no bare times at all, so its calendar has no windows in it
and the refusal file says why for each of the five.

How it was verified

ruff check, ruff format --check, mypy (strict, 28 files), pytest — all
green, coverage 94.32% against an 85% floor. 42 new tests. No golden file or
baseline changed.

Negative controls, each read back out of the file before the gate ran, then
restored from a pre-edit byte copy (diff clean) and re-run green:

sabotage	gate
residual fence removed (if False:)	red — 2 tests
out-of-grammar day rule approximated as the fourth Friday	red — 4 tests
a missing day type assumed to be every day	red — 2 tests
a partial month range widened to whole months	red
the refusal list dropped from the payload	red

One of these found a real weakness in my own test and it is worth naming.
The first run of the residual sabotage came back green. In every committed
document a residual window happens to carry no start/end, so removing the
residual fence just let the next fence catch it — the test was asserting the
outcome, not the fence. I added a synthetic residual window that does carry
hours and a day type, plus a test that the refusal names exclusion rather than a
missing time. With those, the sabotage goes red. The fence is now gated; before,
it was decoration that happened to be correct.

Closes #57

Prepared with AI assistance; reviewed before submission.