feat(voice-packs): tracked tunables, the bats seam, and its wiring

scripts/voice-packs.env carries the decisions worth a diff and nothing
else: the pack list, each voice's source file, crop offset, crop length
and pinned source digest, the extractor path with its engine repo and
commit, and the artifact arithmetic. Paths and numbers only — the pack
directories themselves stay host state under /home/dank/voices.

tests/voice_pack_unit.bats pins behaviour, from inputs to observable
output: a crop inside the first ten seconds exits nonzero naming the
invariant and creates nothing, a legal one builds the whole pack, the
reference comes out 24 kHz mono inside 18-25 s (ffprobe, on a locally
generated tone), the manifest round-trips through jq with offsets and a
sha256 that matches the source bytes, a re-run without --force leaves
every byte untouched, --force retires rather than deletes, --dry-run
needs no extractor at all, and a stub extractor that changed its artifact
size cannot publish a voice. No engine binary, no GPU, no network, no
fleet host: qwen-codec is stood in by a stub with the real tool's I/O
shape, the way frank_tts_unit.bats drives its backends.

test-changed.sh routes both new paths to that seam instead of letting
them land on the generic scripts/* syntax fallback.

scripts/test-changed.sh

@@ -229,6 +229,14 @@ for path in "${CHANGED[@]}"; do
             add_test tests/scripts_syntax.bats
             add_test tests/deployment_scoping.bats
             ;;
+        # The voice-pack builder is the only thing that enforces the 10-second
+        # source-material invariant and the artifact sizes the packs are pinned
+        # to, so it selects its own seam rather than landing on the generic
+        # scripts/* syntax fallback. This case has to precede that fallback.
+        scripts/build-voice-pack.sh|scripts/voice-packs.env)
+            add_test tests/voice_pack_unit.bats
+            add_test tests/scripts_syntax.bats
+            ;;
         scripts/*)
             add_test tests/scripts_syntax.bats
             ;;