fix: add openrouter feature flag to resolve clippy warnings

Add missing openrouter feature flag to terraphim_middleware Cargo.toml.
This resolves unexpected cfg condition value warnings in test files.

Note: Workspace has pre-existing clippy warnings unrelated to this fix
(unused variables, clamp patterns). All security test files pass clippy clean.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: AlexMikhalev

crates/terraphim_middleware/Cargo.toml

@@ -58,3 +58,5 @@ mcp-sse = ["reqwest-eventsource"]
 mcp = ["mcp-sse"]
 # Optional: use rust-sdk for full protocol clients
 mcp-rust-sdk = ["mcp-client", "mcp-spec", "mcp-sse"]
+# OpenRouter LLM provider support
+openrouter = []