Merge step (j): update tests + legacy-cleanup registries for deleted agents

Fork deleted 9 ce-* reviewer agents in step (c.1) and dropped the ce-dhh-
rails-style skill in step (c.2). Tests and legacy-cleanup registries
needed corresponding updates.

Tests:
- tests/review-skill-contract.test.ts: drop ce-dhh-rails-reviewer,
  ce-kieran-rails-reviewer, and ce-data-migration-expert from persona list
  tests. Remove the data-migration-expert unstructured-format test.
- tests/legacy-cleanup.test.ts: switch the .agent.md copilot-format test
  to use agents that still have ce-* versions (correctness-reviewer,
  maintainability-reviewer) since security-sentinel and performance-oracle
  are gone. Drop the `lint` case from legacy-only cleanup since the fork
  re-introduced ce-lint (Python linter) as a current agent.

Legacy cleanup registries:
- src/utils/legacy-cleanup.ts: add the 9 deleted ce-* agent names to
  STALE_AGENT_NAMES and ce-dhh-rails-style to STALE_SKILL_DIRS so upgrades
  from pre-merge installs sweep the old files.
- src/data/plugin-legacy-artifacts.ts: mirror the additions in the
  compound-engineering plugin's historical artifact lists.

Frontmatter:
- Drop embedded <example>/<commentary> blocks from ce-python-package-
  readme-writer.agent.md and ce-tiangolo-fastapi-reviewer.agent.md
  descriptions. Cowork's plugin validator rejects bare angle-bracket
  tokens; tests/frontmatter.test.ts was failing on these two local agents.

Test state: 944 pass / 9 fail. Remaining 9 failures are pre-existing
detect-project-type.sh monorepo probe tests in ce-polish-beta that were
failing on baseline HEAD before this merge work began. Not introduced
by this merge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugins/compound-engineering/agents/ce-python-package-readme-writer.agent.md

@@ -1,6 +1,6 @@
 ---
 name: ce-python-package-readme-writer
-description: "Use this agent when you need to create or update README files following concise documentation style for Python packages. This includes writing documentation with imperative voice, keeping sentences under 15 words, organizing sections in standard order (Installation, Quick Start, Usage, etc.), and ensuring proper formatting with single-purpose code fences and minimal prose.\n\n<example>\nContext: User is creating documentation for a new Python package.\nuser: \"I need to write a README for my new async HTTP client called 'quickhttp'\"\nassistant: \"I'll use the python-package-readme-writer agent to create a properly formatted README following Python package conventions\"\n<commentary>\nSince the user needs a README for a Python package and wants to follow best practices, use the python-package-readme-writer agent to ensure it follows the template structure.\n</commentary>\n</example>\n\n<example>\nContext: User has an existing README that needs to be reformatted.\nuser: \"Can you update my package's README to be more scannable?\"\nassistant: \"Let me use the python-package-readme-writer agent to reformat your README for better readability\"\n<commentary>\nThe user wants cleaner documentation, so use the specialized agent for this formatting standard.\n</commentary>\n</example>"
+description: "Use this agent when you need to create or update README files following concise documentation style for Python packages. Writes documentation with imperative voice, keeps sentences under 15 words, organizes sections in standard order (Installation, Quick Start, Usage, etc.), and uses single-purpose code fences with minimal prose. Use when creating a README for a new Python package, reformatting an existing README for scannability, or enforcing a concise documentation standard across a repo."
 model: inherit
 ---