feat: standalone calendar overrides (calendar.h) + document customization

Add a compile-time override table for MINOR local calendar changes, standalone
(no lectio, no toolchain): edit calendar.h (copied from calendar.def.h), add a
{ month, day, colour, "name" } row, make. It replaces a fixed date's name and
colour, every year, in both single-day and --month output. Limits (no engine):
fixed dates only; name/colour only, not readings or rank/precedence; an override
wins unconditionally.

README gains a "Customize the calendar" section documenting both tiers with
their limits: the standalone override above, and -- for readings, ranks and
movable feasts -- regenerating gen/ from a lectio calendar layer via
clectio-gen (-caldir/-use), then rebuilding with CORPUS= to repack any newly
cited verses, with a git-checkout revert note.

Both forms build clean under -Wall -Wextra; binary unchanged at 666 KB; default
(empty override table) output is unchanged.

Claude-Session: https://claude.ai/code/session_01S1CD1u3tgSS4xNu6WHfp5a

1 files changed, 4 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index ae74a05..c22556a 100644
--- a/Makefile
+++ b/Makefile
@@ -23,6 +23,9 @@ all: clectio
 config.h:
 	cp config.def.h config.h
 
+calendar.h:
+	cp calendar.def.h calendar.h
+
 mktext: mktext.c
 	$(CC) $(CFLAGS) -o $@ mktext.c
 
@@ -42,7 +45,7 @@ endif
 text.lz.h: bin2h text_$(FORM).lz
 	./bin2h text_$(FORM).lz > $@
 
-clectio: clectio.c puff.c puff.h config.h text.lz.h gen/liturgy_$(FORM).h
+clectio: clectio.c puff.c puff.h config.h calendar.h text.lz.h gen/liturgy_$(FORM).h
 	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ clectio.c puff.c
 
 size: clectio