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

[michaelbship]

@cdecker we will follow this up with a doc fix as well

[cdecker]

Rebased on top of main. Changes during rebase:

• Fixed all callers added on main since the original PR (credentials.rs, input.rs, lib.rs, logging.rs, node.rs) — they used old tuple-style Error::Other(...) / Error::Rpc(...) etc. and now use the new constructor methods (Error::other(), Error::rpc(), Error::duplicate_node(), etc.)
• Removed the stray bindings/glsdk.py — Python bindings belong in glsdk/, other languages in bindings/
• Moved all derived files (glsdk.py + Kotlin/Swift/Ruby) into the second commit, keeping commit 1 purely Rust source changes
• Regenerated glsdk.py from the updated Rust definitions