chore(release): prepare v0.6.3

[dpaluy]

Summary

• Bump Fizzy CLI from 0.6.2 to 0.6.3.
• Document that card create/update --body accepts raw HTML.
• Keep the release diff limited to the version and changelog files.

Verification

• Local Ruby 4.0.3: bundle exec rake — 114 runs, 262 assertions, 0 failures, 0 errors, 0 skips; RuboCop inspected 39 files with no offenses.
• bundle exec rake yard — generated documentation for 21 files; 14.17% documented.
• gem build fizzy-cli.gemspec --output /tmp/fizzy-cli-0.6.3.gem — built fizzy-cli 0.6.3 successfully.
• Built-gem metadata/data inspection — no Gemfile.lock entry.
• ruby -c bin/fizzy and ruby -c lib/fizzy/version.rb — Syntax OK; version check reports 0.6.3.
• bundle exec bin/fizzy help — completed successfully.
• git diff --check — clean.

This PR prepares the release only. It must not be merged, tagged, or published by this maintenance job.