sdk: Stable numeric error codes for i18n support

[cdecker]

Summary

• Replace gl-sdk tuple-style error variants with named-field variants carrying code: i32, message: String, and values: HashMap<String, String>
• Each error has a stable numeric code (1000-1099 node identity, 1100-1199 credentials, 2000-2099 RPC, 3000-3099 validation, 9000-9099 generic) enabling host-language i18n lookup
• The values map provides structured interpolation keys so callers can fill translated templates (e.g., "Node {node_id} already exists")
• Constructor functions (Error::rpc(), Error::other(), etc.) keep call sites clean
• Regenerated Python, Kotlin, Swift, and Ruby bindings — all expose .code, .message, .values on error subclasses

Test plan

• cargo build -p gl-sdk compiles cleanly
• Verified generated Python bindings have code, message, values attributes on all Error subclasses
• Verified generated Kotlin bindings have val code: Int, val message: String, val values: Map<String, String>
• Verified generated Swift bindings have code: Int32, message: String, values: [String: String]
• Integration test with host-language error catching and i18n template interpolation

🤖 Generated with Claude Code