Add code-agent-sdk crate and implement code tool subcommands

- Added code-agent-sdk crate with workspace dependencies
- Created internal ApiSymbolKind enum to replace lsp_types in public API
- Added RenameResult type with edit counts for clean API
- Implemented SearchSymbols, FindReferences, GotoDefinition, RenameSymbol, FormatCode
- Updated MCP server and CLI to use internal types
- All compilation successful, 25/45 Phase 12 tasks complete

Author: kennvene-aws

Cargo.lock

@@ -1,6 +1,6 @@
 [workspace]
 resolver = "3"
-members = ["crates/amzn-codewhisperer-client", "crates/amzn-codewhisperer-streaming-client", "crates/amzn-consolas-client", "crates/amzn-qdeveloper-streaming-client", "crates/amzn-toolkit-telemetry-client", "crates/aws-toolkit-telemetry-definitions", "crates/chat-cli", "crates/semantic-search-client"]
+members = ["crates/amzn-codewhisperer-client", "crates/amzn-codewhisperer-streaming-client", "crates/amzn-consolas-client", "crates/amzn-qdeveloper-streaming-client", "crates/amzn-toolkit-telemetry-client", "crates/aws-toolkit-telemetry-definitions", "crates/chat-cli", "crates/code-agent-sdk", "crates/semantic-search-client"]
 default-members = ["crates/chat-cli"]
 
 [workspace.package]

Cargo.toml

@@ -43,6 +43,7 @@ chrono.workspace = true
 clap.workspace = true
 clap_complete.workspace = true
 clap_complete_fig.workspace = true
+code-agent-sdk = { path = "../code-agent-sdk" }
 color-eyre.workspace = true
 color-print.workspace = true
 convert_case.workspace = true