Fix WordPress Coding Standards CI check

[apermo]

Summary

Makes the WordPress Coding Standards and Plugin Check CI jobs pass.

Coding Standards (3 errors)

• Add a project .phpcs.xml.dist ruleset that extends the WordPress
  standard and excludes WordPress.Files.FileName.InvalidClassFileName.
  The plugin ships as a single bootstrap file named after the plugin
  (rt-plugin-report.php); renaming it to class-*.php would break the
  entry point, so this sniff does not apply. The ruleset also configures
  the text domain (plugin-report) and global prefixes.
• Point the CI WPCS step at the ruleset (standard: .phpcs.xml.dist).
• Exclude .phpcs.xml.dist from the distributed plugin zip via .distignore.
• Convert the two else { if (...) } blocks in render_table_row() to
  elseif, resolving Universal.ControlStructures.DisallowLonelyIf. This
  also removes the two // phpcs:ignore comments that never took effect —
  they were placed on the if line, but the sniff reports the violation on
  the else line above. Behaviour is unchanged.

Plugin Check (hidden_files / application_files errors)

Plugin Check scans the raw repo checkout, so it flagged .wp-env.json and
.phpcs.xml.dist as hidden/application files (.dist is a flagged
extension). Both are development-only files already excluded from the
distributed plugin via .distignore, so the Plugin Check step now excludes
them with exclude-files. Only ERROR-type results fail the action, so the
remaining warnings (restricted term "plugin" in the name/slug, the
RT_Plugin_Report prefix, auto-update detection, .github directory) are
non-blocking and left untouched — they reflect the established, published
plugin and aren't introduced here.

⚠️ Rebase note

This branch is cut from current develop. Several other open PRs touch
rt-plugin-report.php (e.g. #92). Please rebase this branch once those are
merged so the elseif refactor applies on top of the final line numbers and
avoids conflicts. Kept as a draft until then.

Disclosure

Claude (Anthropic) assisted with diagnosing the CI failures and preparing this
change. I (the human author) reviewed it and take responsibility for the
contribution.