Update docs, CI, and release tooling for current feature set

[WeekendSuperhero]

Summary

• README.md: Updated MCP tools (17 → 21), prompts (5 → 6), CLI commands, and architecture diagram to reflect current codebase. Added cross-references to DESIGN.md and MCP.md.
• DESIGN.md: Updated tool/prompt counts, removed stale tools (set_flag_color, get_messages_by_uid), added new tools (rank_list_id, delete_list_id), added list-id-cleanup prompt.
• MCP.md: Updated tool/prompt counts, added rank_list_id and delete_list_id with output schemas, removed non-existent set_flag_color, added list-id-cleanup prompt.
• LICENSE: Added Apache License 2.0 (matching Cargo.toml declarations).
• CI: Added windows-latest to the build matrix for cross-platform coverage.
• Release: Added cross-platform binary builds (linux x86_64/aarch64, macOS x86_64/aarch64/universal, Windows x86_64) and GitHub Release creation with softprops/action-gh-release.

Test plan

• CI passes on all three platforms (ubuntu, macos, windows)
• Verify cargo doc builds without warnings
• Verify release workflow produces correct artifacts on a test tag