stacks/index-tts: install git-lfs in image so examples come down real

The IndexTTS-2 repo stores examples/emo_*.wav and examples/voice_*.wav
as Git LFS objects. v1 of our image cloned the repo without an LFS
pull, leaving those paths as ~130-byte pointer text files — unusable
for `docker cp` into /worktank/index-tts/{voices,emotions}/ as starter
references. (Caught when an emotion_voice="hate" call returned audio
that was actually the pointer text round-tripped through file IO.)

v2 adds git-lfs to the apt list, calls `git lfs install --system`
once, and `git lfs pull` after the checkout. Adds ~1-2 MB to the
image (the examples are small audio clips). INDEX_TTS_TAG bumped to
v2 to force a clean rebuild.

stacks/index-tts/.env.example

@@ -6,8 +6,10 @@
 INDEX_TTS_SHA=830f6f8f94a51fea23ab1d639027a86200075a4e
 
 # Local image tag — bump when you change build context (Dockerfile,
-# app.py, entrypoint.sh) to force a fresh layer build.
-INDEX_TTS_TAG=v1
+# app.py, entrypoint.sh) to force a fresh layer build. v2 = git-lfs
+# added so the example WAVs in /opt/index-tts/examples/ come down as
+# real audio (v1 left them as LFS pointer stubs).
+INDEX_TTS_TAG=v2
 
 # ── network ──────────────────────────────────────────────────────────
 # Host port. Container listens on 8000 internally.