It enabled nothing — the agent layer is always built — yet the README,
QUICKSTART and USE_CASES told people to pass it. Removed, with those
snippets fixed: they now depend on the git repository (nothing is on
crates.io, so `version = "2.0"` never resolved) and USE_CASES no longer
presents the `float16` feature as half-precision storage (that is
MemoryConfig::float16, on by default for new stores).
Breaking for anyone passing `features = ["agent"]`: drop it.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
