Untrack uv.lock and loosen livekit-agents version constraint

uv.lock should not be tracked in the template (enforced by
template-check.yml CI). Also change livekit-agents from ==1.6.0 to
>=1.6.0 so the starter picks up newer compatible releases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: royalfig

pyproject.toml

@@ -9,7 +9,7 @@ description = "Simple voice AI assistant built with LiveKit Agents for Python"
 requires-python = ">=3.10, <3.15"
 
 dependencies = [
-    "livekit-agents==1.6.0",
+    "livekit-agents>=1.6.0",
     "livekit-plugins-ai-coustics~=0.2",
     "python-dotenv",
 ]