self-review should just use the same setup as everything else

[derekmisler]

Summary

Simplify the self-review workflow by removing the complex cross-workflow artifact passing logic. The resolve-context job and its associated artifact handling are eliminated, and the review job now uses the same straightforward setup as other workflows in the repository.

Closes: https://github.com/docker/gordon/issues/560

Changes

• Removed resolve-context job — eliminated 200+ lines of artifact download, parsing, and context resolution logic
• Simplified review job — removed dependency on resolve-context outputs; now directly handles PR number resolution from event context
• Removed workflow_dispatch trigger — no longer needed with simplified context handling
• Updated workflow names — renamed "PR Review Trigger" to "Self PR Review - Trigger" for clarity
• Added review_requested trigger — trigger workflow when a review is explicitly requested
• Removed reply-to-feedback job — eliminated complex thread context building and artifact handling for reply logic

The workflow now uses the same event-driven approach as the rest of the codebase, reducing maintenance burden and improving reliability.