BOG-258: Bump kis-sdk to 0.2.0 and clean usage docs

[Bogyie]

Summary

• Bump the kis-sdk crate and lockfile package version to 0.2.0.
• Update README and English/Korean usage docs to focus on real read-client setup and version 0.2 dependency examples.
• Remove user-facing mock server, mock order, and real-to-mock fallback walkthroughs while preserving mock references only in developer contract/test-harness context.
• Update the crates publish guard example to kis-sdk 0.2.0.

Validation

• git diff --check
• cargo metadata --locked --format-version 1 --no-deps
• python3 scripts/verify-crates-publishable.py
• cargo fmt --check
• cargo doc --locked --no-deps
• cargo test --locked

QA Evidence

• Multica QA retest for BOG-258 passed after the README mock/fallback cleanup.
• Confirmed the top-level README no longer exposes Real-to-mock fallback or a standalone Mock Server section.
• Confirmed README.md, docs/usage.md, and docs/usage-ko.md no longer contain user-flow instructions for running the local mock server, creating mock clients, mock orders, mock fixture scenarios, or real-to-mock fallback.

Release Notes

• This PR does not publish crates, create a release tag, or merge to main.
• Actual crates.io publish remains gated by the authorized tag, crates-io environment, and CARGO_REGISTRY_TOKEN workflow requirements.

[amazon-q-developer]

This PR successfully bumps the kis-sdk version from 0.1.0 to 0.2.0 and cleans up documentation by removing user-facing mock server references. The changes are consistent across all files:

• Version updates in Cargo.toml and Cargo.lock are properly synchronized
• Documentation correctly updated from 0.1 to 0.2 version references
• Branch references updated from bog-220-kis-sdk to main
• Mock server usage examples removed from user-facing docs while preserving developer test harness documentation

All changes are documentation and metadata updates with no functional code modifications. No blocking issues identified.

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