fix hosted issue trigger gating

[romgenie]

Summary

• ignore plain issues.opened deliveries so newly submitted issues do not start Cody work automatically
• gate issue/comment routing against webhook-style enabled_triggers values such as issues.labeled and issue_comment.created
• keep explicitly labeled coven:fix issues routing to fix_issue

Root cause

The hosted adapter was accepting issues.opened as a work trigger even though the policy for the repository only enabled issues.labeled, issue_comment.created, and pull_request_review_comment.created. That caused OpenCoven/coven-cave#2892 to publish a failure comment for a normal diagnostic issue submission.

Validation

• python -m unittest deploy.coven-github.test_coven_github_adapter
• python -m py_compile deploy\\coven-github\\coven_github_adapter.py
• deployed to webhook.complete.tech and verified synthetic issues.opened is ignored while issues.labeled queues fix_issue

@BunsDev this is the follow-up for the unexpected covencat issue-created run.