feat(cli): expand a leading tilde in KIMI_CODE_HOME

Problem

KIMI_CODE_HOME is returned verbatim by the CLI path helper. A commonly used value such as KIMI_CODE_HOME="~/.local/share/kimi-code" therefore remains a relative path containing a literal ~, instead of resolving under the user's home directory.

This is easy to trigger because environment-variable values are often quoted in shell profiles, where tilde expansion does not occur.

Proposed behavior

Expand only these forms:

• ~ to the current home directory
• ~/... (and the platform separator equivalent) under the current home directory

Keep other values unchanged, including ~user/..., to avoid implementing user-account lookup semantics.

Scope

• centralize the expansion in the CLI data-path helper
• add focused unit tests
• document the supported behavior in the English and Chinese environment-variable references

Start at the centralized CLI data-path helper and inspect the focused unit-test setup. Verify that only ~ and ~/... (with the platform separator equivalent) expand under the current home directory, while other values remain unchanged. Update the English and Chinese environment-variable references, and finish when the tests and both documents cover the supported behavior.