feat(clectio-gen): apply a calendar layer/sanctorale when generating

Add opt-in flags so clectio's tables can be regenerated from a customized
calendar instead of only the embedded universal one:

  clectio-gen -caldir DIR -use a,b [-sanctorale DIR] <new|old> y0 y1 out/

- -caldir + -use stack calendar layers (rank, colour, name, reading.*) over the
  calendar; -sanctorale DIR applies a full of.ini/ef.ini replacement.
- The BOOK table stays hermetic (LECTIO_CONFIG still points nowhere), so the
  generator can't read a stale user books.ini -- calendar customization and the
  book aliases are kept separate concerns.
- config.SetCalendarsDir lets CalendarsDir be pointed at an explicit layer dir
  without a full config tree (and without an unrelated books.ini there).

Verified end to end: a layer adding a feast with a proper gospel regenerates
into liturgy_of.h + verses_of.keys, and the rebuilt clectio shows it. Default
(no flags) output is byte-identical to before. make test green.

1 files changed, 14 insertions, 1 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index a225a12..cd32c90 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -324,9 +324,22 @@ func configPath() (path string, isDefault bool, err error) {
 	return filepath.Join(dir, "lectio", "config.ini"), true, nil
 }
 
+// calendarsDirOverride, when set, is returned by CalendarsDir verbatim,
+// bypassing the config-relative default. It lets a tool (e.g. clectio-gen) apply
+// calendar layers from an explicit directory without pointing the whole config
+// tree -- and without picking up an unrelated books.ini -- at that location.
+var calendarsDirOverride string
+
+// SetCalendarsDir overrides the directory CalendarsDir returns. Empty (the
+// default) restores the config-relative <config dir>/calendars.
+func SetCalendarsDir(dir string) { calendarsDirOverride = dir }
+
 // CalendarsDir returns the directory holding user calendar-layer files
-// (<config dir>/calendars).
+// (<config dir>/calendars, unless overridden by SetCalendarsDir).
 func CalendarsDir() (string, error) {
+	if calendarsDirOverride != "" {
+		return calendarsDirOverride, nil
+	}
 	p, _, err := configPath()
 	if err != nil {
 		return "", err