Raise GREEN_THRESHOLD to 100 so only fully covered files rate green

[cesarjr]

Closes #13

Summary

Why: a file at 66.66% coverage rated 🟢 and passed the --fail-on-low-coverage gate, which made the green rating misleading — a file could be marked green with a third of it untested.

• Raise Parser::GREEN_THRESHOLD from 66.66 to 100: 🟢 (and bg-success in the HTML report) now means the file is fully covered, and --fail-on-low-coverage exits 1 for any reported file below 100%. RED_THRESHOLD is unchanged, so 🟡 now spans 33.34%–99.99%.
• Compare the unrounded covered_percent in low_coverage_files, percentage_indicator, and percentage_bar_color, so a file at e.g. 99.996% no longer rounds up to 100% and slips past the gate.
• Display percentages with two decimal places in all cases (e.g. 60.00%), flooring instead of rounding, so a partially covered file never displays as 100.00% — a 99.996% file shows 99.99%, rates 🟡, and fails the build.
• Update README (rating bands, gate docs, report example), add a 0.9.0 CHANGELOG entry flagging the breaking change, and bump the version to 0.9.0.
• No change needed in lib/couve.rb: the stderr message and --help text interpolate the constant and now read "below 100%".

How to test

• bundle exec rspec — 37 examples, 0 failures (developed with strict TDD: every behavior change landed as a failing spec first).
• bundle exec rubocop — no offenses.
• bundle exec exe/couve spec/fixtures/codeclimate.json tmp/report.md --fail-on-low-coverage — exits 1, prints couve: coverage below 100% in ..., and the report rates the 60.00%/83.33%/93.33% files 🟡.

Notes

Behavioral consequence worth knowing: the default (project-wide) report already hides fully covered files, so with this change every reported file is 🔴/🟡 and --fail-on-low-coverage fails whenever the report is non-empty. In practice the flag pairs with --changed-files, where a fully covered changed-file set still passes; this is now documented in the README. Released as 0.9.0 since it changes the gate behavior for existing users.

🤖 Generated with Claude Code