docs: fix README discrepancies and cleanup outdated docs

[myaple]

This PR addresses discrepancies in the documentation identified during a deep dive.

Changes:

1. Documentation Cleanup: Deleted GITLAB_API_CONSOLIDATION_ANALYSIS.md. This file contained a roadmap for refactoring the GitLab API client. A review of src/gitlab.rs confirmed that all proposed changes (consolidating search, issue fetching, note fetching, and label operations) have been implemented. The document was therefore outdated and misleading.
2. License Fix: The README.md and badges claim the project is MIT licensed, but the repository was missing a LICENSE file and the license field in Cargo.toml. Added standard MIT License text to LICENSE and updated Cargo.toml.
3. README Clarification: Updated README.md to clarify that slash commands must follow the bot mention (e.g., @gitbot /plan) to be correctly parsed, as the parser expects the command to be in the text after the mention.
4. Symlink Restoration: Restored CLAUDE.md as a symbolic link to AGENTS.md, preserving the project structure.

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PR created automatically by Jules for task 8665293062200874617 started by @myaple

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[myaple]

Can you double check all the command line arguments and descriptions in the reader specifically? Are any outdated?

[google-labs-jules]

Can you double check all the command line arguments and descriptions in the reader specifically? Are any outdated?

I have double-checked all command line arguments and descriptions in src/config.rs against README.md. I verified that all 33 configuration fields defined in the AppSettings struct are correctly documented in the README tables, including their flags, environment variables, default values, and descriptions. No discrepancies were found.