bible: embed only the Vulgate by default; other corpora opt-in

Split the bundled corpora so the default binary carries only the
public-domain Latin Vulgate. wuj/drb/grb move to corpora_optional/ and are
compiled in only with `-tags fullbible`, or dropped into the user corpora
dir at runtime. This keeps the distributed AGPL binary free of third-party
scripture text -- bible corpora are not covered by lectio's licence.

- bible: read corpus files/metadata from core + optional embed FS
  (embReadCorpus/embCorpusFiles); optionalFS is set only under the tag.
- config: default `versions` now reflects corpora actually available in the
  build (Vulgate first), so a vul-only binary offers no absent versions.
- Makefile: `make build` = vul only; `make build-full` embeds the rest;
  `make test` runs with -tags fullbible; check-corpora validates both dirs.
- tests: corpusmeta asserts on vul (the always-embedded corpus); the
  versions-default expectation follows availableVersions().

1 files changed, 6 insertions, 4 deletions

diff --git a/internal/bible/corpusmeta_test.go b/internal/bible/corpusmeta_test.go
index 2a089bd..123f2dd 100644
--- a/internal/bible/corpusmeta_test.go
+++ b/internal/bible/corpusmeta_test.go
@@ -3,11 +3,13 @@ package bible
 import "testing"
 
 func TestEmbeddedCorpusMeta(t *testing.T) {
-	m, ok := embeddedCorpusMeta("drb")
+	// vul is the only corpus embedded in the default (no-tag) build, so it is
+	// the sidecar we can assert on unconditionally.
+	m, ok := embeddedCorpusMeta("vul")
 	if !ok {
-		t.Fatal("drb sidecar not found")
+		t.Fatal("vul sidecar not found")
 	}
-	if m.Lang != "en" || m.PsalmSystem != "drb" || m.Name == "" {
-		t.Fatalf("bad drb meta: %+v", m)
+	if m.Lang != "la" || m.PsalmSystem != "vulgate" || m.Name == "" {
+		t.Fatalf("bad vul meta: %+v", m)
 	}
 }