[0.1.5] Use project Ruby SDK for all bundle exec docscribe commands

[unurgunite]

Description

All bundle exec docscribe commands now run through the project's Ruby SDK instead of the system PATH Ruby. Previously, only the server startup path (ruby -e in startServerProcess()) used the SDK — the CLI fallback and gem check both ran bundle from the system PATH, potentially using a different Ruby version or gem set.

Changes

• DefaultCommandExecutor — new environment: Map<String, String> constructor parameter, forwarded to GeneralCommandLine.withEnvironment(). Backward compatible (defaults to empty map).
• buildSdkEnvironment() — new helper in DocscribeDaemon that resolves the Ruby SDK path via rubyCommand(), prepends SDK bin/ to PATH, and sets BUNDLE_GEMFILE.
• performGemCheck() — applies SDK environment to ProcessBuilder so bundle exec docscribe --version uses the SDK Ruby.
• fallback() — passes SDK environment to DefaultCommandExecutor so the CLI wrapper uses the SDK Ruby.
• startServerProcess() — refactored to reuse buildSdkEnvironment() instead of inline env setup, reducing duplication.

Checklist

• Tests pass (./gradlew test)
• Formatting clean (./gradlew spotlessCheck)
• Static analysis clean (./gradlew detekt)
• Plugin verified (./gradlew verifyPlugin)
• CHANGELOG updated