feat(config): reading_lang/reading_version + ReadingCorpus resolver

Task 3 of national-bibles. Adds reading_lang (any language code) and
reading_version (explicit corpus code) config fields, setField cases,
renderConfigINI lines + self-documenting header, and Config.ReadingCorpus():
reading_version > reading_lang match > ui_language match > "" (Latin fallback
applied by the caller).

Also adds an `autoselect` corpus-metadata flag (default true), surfaced during
this task: the built-in wuj declares lang=pl, so lang-auto would have
re-selected the incomplete Wujek for Polish users and defeated the wuj-drop.
wuj.ini now sets autoselect=false, so it is reachable only via an explicit
reading_version or --ref; the resolver's language auto-match skips
non-autoselectable corpora. A corrected Wujek drop-in (autoselect defaults
true) auto-serves Polish with zero config.

1 files changed, 20 insertions, 0 deletions

diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index e3af475..3830cb6 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -301,3 +301,23 @@ func TestPartShown(t *testing.T) {
 		t.Error("ewangelia not mentioned should still be shown")
 	}
 }
+
+func TestReadingCorpusResolution(t *testing.T) {
+	// drb is an embedded corpus with lang=en.
+	c := Config{ReadingVersion: "drb"}
+	if got := c.ReadingCorpus(); got != "drb" {
+		t.Fatalf("explicit reading_version: got %q", got)
+	}
+	c = Config{ReadingLang: "en"}
+	if got := c.ReadingCorpus(); got != "drb" {
+		t.Fatalf("reading_lang match: got %q", got)
+	}
+	c = Config{UILanguage: "en"}
+	if got := c.ReadingCorpus(); got != "drb" {
+		t.Fatalf("ui_language fallback: got %q", got)
+	}
+	c = Config{UILanguage: "pl"} // no pl corpus embedded
+	if got := c.ReadingCorpus(); got != "" {
+		t.Fatalf("no match should be empty: got %q", got)
+	}
+}