feat(cli): --month, --date and --today narrow a report

--pretty made a report readable and, in the same stroke, ungreppable: a box
spans seven lines, so `grep 2026-03-` returns fragments of March rather than
March. The nearest working equivalent is a paragraph-mode awk incantation that
depends on the boxes happening to be blank-line separated -- knowledge no
reader should need to select a month.

The three flags are ALTERNATIVES, not a stack. Naming two exits 2 rather than
letting one quietly win, the same discipline the positional year and --year
already follow, and the same reason this program refuses a flag it cannot
honour instead of accepting and ignoring it.

--date and --today CARRY a year, so the year becomes optional on those two and
required only after the window has had its say: `colitur day --today` is a
complete command while `colitur day` still is not. A year named alongside them
must agree. The disagreement message names the flag rather than printing two
bare numbers, because with --today the second year appears nowhere on the
command line for the reader to trace.

temporal refuses --year yet accepts --date/--today including as its year
source. That is not a back door to the refused spelling: --year is a second
spelling of the positional year, which temporal deliberately does not offer,
whereas --date selects a DAY and merely happens to determine which year
contains it.

The window is a predicate over an ISO date STRING rather than over a Date.t,
because the two report shapes reach it differently -- resolved days carry a
Date.t, temporal_report carries a flat Record whose date is already text --
and one shared test is one implementation rather than two that can drift.

Accepted by day, readings, rubrics and temporal; refused by easter, emit,
table, render, publish, check, convert, lang, config and new-overlay.

--pretty had shipped undocumented in both --help and colitur(1). Both now
carry it, alongside the new narrowing section; the man page's awk example is
shown precisely so the flag that replaces it is justified.

Default output is byte-identical to 1.1.0 across seven years, five commands
and both rites, and across all five emit formats and the shipped templates.

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