feat(cli): colitur check and colitur new-overlay

Writing a local calendar had no feedback loop. An overlay is applied, not
validated -- that stays true, and the five test layers still cannot vouch for
a user's file -- but before this the only way to learn whether yours did what
you meant was to generate a year of output and grep for your own slug, and the
only way to see that a directive matched nothing was to notice a warning
scroll past among 365 lines.

`check` loads each overlay, applies it to the real shipped calendar, and
reports the directive counts, the slug each one targets, and any directive
that found no target. It exits 2 when a file fails to load or a directive
matched nothing, so it composes into a Makefile or a pre-commit hook rather
than merely being readable. It is applied to the SHIPPED calendar and not to
an empty layer on purpose: against an empty one every Suppress would fail
trivially and the check would be worthless.

It answers three narrow questions -- does the file parse, does every directive
find its target, what does the merged result contain. It does not validate a
calendar against the rubrics and cannot, and both the help text and the man
page say so rather than letting the name imply more than it does.

`new-overlay` prints a starter to stdout for redirection, rather than writing
a file where it likes. Every value in it is a placeholder that will appear in
`day` output if left unedited, so a half-finished overlay is visible rather
than silently inert, and it documents the three date shapes and the legal
values for each closed field inline.

load_ef_layer now returns its diagnostics instead of printing them: day and
readings still want them on stderr beside a year of output, while check wants
them on stdout, attributed to the overlay that produced them, and counted.
Printing at the source made the second impossible.

The cram test round-trips new-overlay through check rather than pinning the
template line by line -- editing its prose should not fail a test, but a
syntax error in it still must.

1 files changed, 21 insertions, 0 deletions

diff --git a/man/colitur.1 b/man/colitur.1
index 8a52858..a637f19 100644
--- a/man/colitur.1
+++ b/man/colitur.1
@@ -65,6 +65,27 @@ occurrence, commemoration and transfer.
 .BI readings " YEAR"
 The Mass reading citations, one line per day.
 .TP
+.B new\-overlay
+Print a starter overlay file to standard output, for redirection. Every value
+in it is a placeholder that will appear in
+.B day
+output if left unedited, so a half\-finished overlay is visible rather than
+silently inert.
+.TP
+.BI check " FILE" ...
+Load each overlay, apply it to the shipped calendar, and report what it does:
+the directive counts, the slug each targets, and any directive that matched
+nothing. Exits
+.B 2
+if a file fails to load or a directive found no target, so it composes into a
+Makefile or a pre\-commit hook. It answers three narrow questions \(em does
+the file parse, does every directive find its target, and what does the merged
+result contain. It does
+.I not
+validate a calendar against the rubrics, and cannot: see
+.B OVERLAYS
+below.
+.TP
 .BI \-\-overlay " FILE"
 Apply a user calendar on top of the shipped one. Repeatable and ordered;
 .B day