refactor: remove owlen-code binary and code-client feature

Remove the separate owlen-code binary as code assistance functionality
is now integrated into the main application through the mode consolidation system.

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

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

crates/owlen-cli/Cargo.toml

@@ -11,18 +11,12 @@ description = "Command-line interface for OWLEN LLM client"
 [features]
 default = ["chat-client"]
 chat-client = ["owlen-tui"]
-code-client = []
 
 [[bin]]
 name = "owlen"
 path = "src/main.rs"
 required-features = ["chat-client"]
 
-[[bin]]
-name = "owlen-code"
-path = "src/code_main.rs"
-required-features = ["code-client"]
-
 [[bin]]
 name = "owlen-agent"
 path = "src/agent_main.rs"