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, 15 insertions, 0 deletions

diff --git a/internal/bible/embed_optional.go b/internal/bible/embed_optional.go
new file mode 100644
index 0000000..abe7b35
--- /dev/null
+++ b/internal/bible/embed_optional.go
@@ -0,0 +1,15 @@
+//go:build fullbible
+
+package bible
+
+import "embed"
+
+// Build with `-tags fullbible` to compile the optional corpora (wuj, drb, grb)
+// into the binary alongside the always-embedded Vulgate. These translations are
+// third-party scripture text and are NOT covered by lectio's AGPL licence; ship
+// a fullbible binary only where redistributing those corpora is permitted.
+//
+//go:embed corpora_optional
+var optionalEmbed embed.FS
+
+func init() { optionalFS = optionalEmbed }