Inherit connector provider plugin paths

[chubes4]

Summary

• Carries inherited connector provider_plugin_paths through sanitized recipe inheritance as providerPluginPaths.
• Merges inherited provider plugin paths into the generated sandbox recipe so the agent step receives the inherited provider plugin slugs.
• Extends generic smoke coverage for provider/model/provider plugin path/secret env name/secret env value inheritance while asserting secret values stay out of recipe JSON.

Tests

• npm run build
• npm run discovery-command-smoke
• npm run wordpress-plugin-smoke
• git diff --check

Closes #394.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Implemented the generic connector inheritance path, added regression coverage, ran focused verification, and prepared the PR summary. Chris remains responsible for review and merge.

[chubes4]

Review worker launched for merge-readiness check: https://discord.com/channels/1493321868415996064/1510860179921698947