caldata: allow an external universal sanctorale to override the embedded one

The universal calendar of saints can now be refreshed or replaced without a
rebuild: if ~/.config/lectio/sanctorale/of.ini (OF) or ef.ini (EF) is present
and parses, caldata.Base uses it instead of the embedded calendar; a missing or
malformed file falls back to the embedded default, so the binary stays
self-contained and correct out of the box. Local diocesan/national additions
keep layering on top via calendars/ + `use` (unchanged). The temporal cycle and
precedence rules stay in code -- only the sanctorale is data.

- caldata.SetSanctoraleDir hook (mirrors bible/naming/i18n); Base() prefers the
  external file per form. config.SanctoraleDir(); wired in the CLI, TUI and web
  entry points. Tests cover override, no-file, and malformed-file fallback.
- README: new "Calendar of saints" section (two tiers: overlay via `use`,
  replace via sanctorale/<form>.ini); config comment notes the override.

1 files changed, 17 insertions, 0 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 08c0b60..0596194 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -49,6 +49,8 @@ const configHeader = `# lectio configuration (INI). Full-line comments only (# o
 #   pager             shell command, e.g. less -R; empty = off
 #   use               calendar layers to stack over the universal calendar: names of
 #                     ~/.config/lectio/calendars/<name>.ini files (comma list, order = precedence)
+#                     (to REPLACE the whole universal calendar instead, drop
+#                      ~/.config/lectio/sanctorale/of.ini or ef.ini -- see the README)
 #
 # [calendar] — computed-calendar placement options (defaults = Universal Roman Calendar):
 #   epiphany          fixed | sunday    (fixed = Jan 6; sunday = the Sunday of Jan 2-8)
@@ -360,6 +362,21 @@ func UIDir() (string, error) {
 	return filepath.Join(filepath.Dir(p), "ui"), nil
 }
 
+// SanctoraleDir is the user directory for an optional external universal
+// sanctorale that REPLACES the embedded one: <dir>/of.ini (Ordinary Form) and
+// <dir>/ef.ini (Extraordinary Form). It lets the calendar of saints and their
+// ranks be refreshed as the Church changes them without rebuilding the binary;
+// absent (the default), the embedded, oracle-validated calendar is used. Local
+// diocesan/national additions layer ON TOP via calendars/ + `use` (they need no
+// full file). Mirrors CalendarsDir.
+func SanctoraleDir() (string, error) {
+	p, _, err := configPath()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(filepath.Dir(p), "sanctorale"), nil
+}
+
 // NamesDir is the user directory for drop-in day-name language files
 // (<code>.ini), alongside calendars/ and corpora/ under the lectio config dir.
 // A file here overrides the built-in day names for its language key by key;