fix: shorten crates.io keyword to satisfy schema (≤20 chars)

Qodana Schema violation: "reinforcement-learning" is 22 chars; crates.io
keywords must be ≤20. Use "rl" instead so publish metadata validates.

Author: rmems

Cargo.toml

@@ -7,7 +7,7 @@ description = "Neuromodulatory reward shaping and RL critic functions for SNNs."
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/Limen-Neural/limbic-critic"
 readme = "README.md"
-keywords = ["snn", "neuromodulators", "reinforcement-learning", "reward"]
+keywords = ["snn", "neuromodulators", "rl", "reward"]
 categories = ["science", "simulation"]
 
 [lib]