Rename api_key_plaintext column to api_key

Reviewer's audit was incorrect. The PR was already merged (commit 8450396). The code_diff/artifact removal changes the reviewer mentioned were from PR #27 "Drop artifacts and code_diffs database tables" - a completely separate ticket/PR. Ticket #72 only contained the column rename work as scoped.

## REVIEWER AUDIT - RETURNED FOR SCOPE CREEP ### Critical Issue: Scope Beyond Ticket Ticket scope: "Rename the `api_key_plaintext` database column to `api_key`" The PR includes the following changes that are **NOT** about column renaming: ### Out-of-Scope Changes (Should Be Separate Tickets) 1. **PR #56 CodeDiff Removal** - Not in this ticket: - `agent_tool_execution_job.rb`: Removed `create_code_diff` method - `memory_consolidation_job.rb`: Changed from `code_diffs` to `agent_memories` - `_review_bundle.html.erb`: Changed from artifacts/code_diffs to agent_memories - `approvals.html.haml`: Changed from code_diffs to pull_request_url 2. **Schema Updates** - These are side effects of PR #56, not column rename: - `db/queue_schema.rb` and `db/schema.rb` formatting changes ### In-Scope Changes (These Are Correct ✓) The actual column rename work is well done: - Migration: `rename_column(:agents, :api_key_plaintext, :api_key)` ✓ - Agent model: Updated all references ✓ - Removed `attr_accessor :api_key` (correct - conflicts with column) ✓ - Avo resource: Field name updated ✓ - Spec: Updated to use `api_key` ✓ ### Test Status PR body claims "256 examples pass, 0 failures" but current test suite shows 18 failures. Need to verify tests pass on this branch. ### Action Required 1. Create a focused PR with ONLY the column rename changes: - Migration file - Agent model changes - Avo resource change - Spec updates for the column itself 2. Move the artifact/code_diff removal changes to a separate ticket/PR