docs: add CLI and configuration references

[minixalpha]

Summary

• Add a bilingual user-documentation index with complete English and Chinese CLI and configuration references.
• Document every current CLI option and default, task input modes, working-directory behavior, output channels, exit statuses, ATIF trajectory rules, and internal Event Journal storage.
• Document configuration sources, supported variables, defaults, settings-file shape, precedence, and empty-value handling.
• Keep both READMEs concise and aligned by replacing detailed reference material with getting-started guidance and direct links.
• Record the user-facing documentation change in the 0.8.x changelog.

Validation

• .venv/bin/pytest — 188 passed
• All local Markdown links in the updated READMEs and new user documentation resolve.
• git diff --check main...HEAD

Closes #32