engines: import f5-tts + kokoro + tortoise sidecars into the tree

The python FastAPI sidecars have lived ad-hoc at /srv/appdata/
<engine>/build/ on the host without version control. Bringing them into
the skald repo so the engine code travels with the cross-engine
routing it depends on.

This commit lands the VANILLA version of each engine on main:

  engines/f5-tts/    SWivid F5-TTS (CC-BY-NC weights flagged)
  engines/kokoro/    hexgrad Kokoro-82M (Apache 2.0 top to bottom)
  engines/tortoise/  neonbjb Tortoise-TTS (Apache 2.0 top to bottom)

Engine-specific kludges (question doubling, GPU coordination,
pause-duration tuning) get layered on engine/* branches per the
README. Main stays the safe-to-read baseline.

engines/f5-tts/compose.yml

@@ -0,0 +1,43 @@
+# F5-TTS standalone stack on the host.
+#
+# License posture (acknowledged 2026-05-13): code is Apache 2.0, but
+# the pretrained model weights are CC-BY-NC (Emilia training data).
+# Personal listen is fine; public sharing is a flagged gray area.
+# Sulkta's call: ship anyway.
+#
+# Runtime: 8GB GPU is plenty (F5 inference ~4-6GB peak).
+#
+# First-run cost: ~2GB model download from HuggingFace into hf-cache,
+# happens on first inference request. Subsequent runs are warm.
+name: f5-tts
+
+services:
+  f5-tts:
+    image: registry.example.local:5000/f5-tts:0.3
+    container_name: f5-tts
+    restart: unless-stopped
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: all
+              capabilities: [gpu]
+    ports:
+      - "127.0.0.1:7792:7860"
+      - "127.0.0.1:7792:7860"
+    volumes:
+      # HF model weights cache — persists ~2GB after first download.
+      - /srv/appdata/f5-tts/hf-cache:/cache/hf
+      # Reference voice clips (lj_speech.wav, etc).
+      - /srv/appdata/f5-tts/voices:/voices:ro
+      # Rendered audio output — skald writes story narrations here.
+      - /srv/appdata/f5-tts/audio:/audio
+    environment:
+      HF_HOME: /cache/hf
+      HF_HUB_DISABLE_TELEMETRY: "1"
+    labels:
+      org.sulkta.domain: "sulkta"
+      org.sulkta.owner: "Sulkta"
+      org.sulkta.managed-by: "compose"
+      org.sulkta.role: "f5-tts"