Add typed KIS parameter helpers

[Bogyie]

Summary

• Add typed account product, domestic stock market division, and cash order division values with helper constructors for safer request building.
• Add typed operation-id newtypes for domestic stock realtime, bond, and domestic futures/options inventory execution paths.
• Keep the existing String request fields, string constants, and &str operation-id methods available for downstream compatibility.
• Merge current main, resolve the README conflict with the BOG-258 user-facing mock cleanup intact, bump kis-sdk to 0.2.1, and update README plus English/Korean usage docs for the typed API path.

Verification

• QA: cargo fmt --check passed
• QA: cargo test --locked passed (mock_server_contract 4 passed, sdk_core 45 passed, doc-tests 0 passed)
• QA: cargo metadata --locked --format-version 1 --no-deps passed and confirmed kis-sdk 0.2.1
• QA: python3 scripts/verify-crates-publishable.py passed (Publishable crates.io package(s): - kis-sdk 0.2.1)
• QA: git diff --check --cached passed
• QA: cargo doc --locked --no-deps passed
• QA: conflict marker grep passed (<<<<<<<, =======, >>>>>>> not found)
• Earlier typed-path QA: cargo test --locked typed_ --test sdk_core passed (2 passed), and static API compatibility confirmed existing Account::new, String request fields, &str operation-id methods, and string constants were not removed

Coordination

• Related Multica issue: BOG-259
• BOG-258 conflict check: README/user-guide cleanup remains in place. Remaining mock/tryitout references are limited to tests, contract/developer mock-server docs, or explanations that tryitout endpoints are not live WebSocket subscription APIs.
• Live KIS API calls were not run because they are outside the issue scope.

[amazon-q-developer]

The typed KIS parameter helpers implementation is well-designed and maintains backward compatibility. The PR successfully adds type safety for account products, market divisions, and cash order divisions while preserving existing string-based APIs. All 49 tests pass, demonstrating comprehensive coverage of the new functionality. The changes follow Rust best practices with proper trait implementations (Display, FromStr, Serialize) and validation logic.

---

You can now have the agent implement changes and create commits directly on your pull request's source branch. Simply comment with /q followed by your request in natural language to ask the agent to make changes.