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>

tests/review-skill-contract.test.ts

@@ -384,8 +384,6 @@ describe("ce-code-review contract", () => {
       "ce-adversarial-reviewer",
       "ce-cli-readiness-reviewer",
       "ce-previous-comments-reviewer",
-      "ce-dhh-rails-reviewer",
-      "ce-kieran-rails-reviewer",
       "ce-kieran-python-reviewer",
       "ce-kieran-typescript-reviewer",
       "ce-julik-frontend-races-reviewer",
@@ -414,8 +412,6 @@ describe("ce-code-review contract", () => {
     )
 
     for (const agent of [
-      "ce-dhh-rails-reviewer",
-      "ce-kieran-rails-reviewer",
       "ce-kieran-python-reviewer",
       "ce-kieran-typescript-reviewer",
       "ce-julik-frontend-races-reviewer",
@@ -423,21 +419,10 @@ describe("ce-code-review contract", () => {
       expect(content).toContain(agent)
       expect(catalog).toContain(agent)
     }
-
-    expect(content).toContain("## Language-Aware Conditionals")
-    expect(content).not.toContain("## Language-Agnostic")
   })
 
   test("stack-specific reviewer agents follow the structured findings contract", async () => {
     const reviewers = [
-      {
-        path: "plugins/compound-engineering/agents/ce-dhh-rails-reviewer.agent.md",
-        reviewer: "dhh-rails",
-      },
-      {
-        path: "plugins/compound-engineering/agents/ce-kieran-rails-reviewer.agent.md",
-        reviewer: "kieran-rails",
-      },
       {
         path: "plugins/compound-engineering/agents/ce-kieran-python-reviewer.agent.md",
         reviewer: "kieran-python",
@@ -469,15 +454,11 @@ describe("ce-code-review contract", () => {
     }
   })
 
-  test("leaves data-migration-expert as the unstructured review format", async () => {
-    const content = await readRepoFile(
-      "plugins/compound-engineering/agents/ce-data-migration-expert.agent.md",
-    )
-
-    expect(content).toContain("## Reviewer Checklist")
-    expect(content).toContain("Refuse approval until there is a written verification + rollback plan.")
-    expect(content).not.toContain("Return your findings as JSON matching the findings schema.")
-  })
+  // Fork-specific: data-migration-expert, dhh-rails-reviewer, kieran-rails-reviewer,
+  // design-implementation-reviewer, design-iterator, figma-design-sync,
+  // performance-oracle, security-sentinel, and ankane-readme-writer were removed
+  // from the fork (see commit 25543e6). Upstream's generated versions are deleted
+  // in this merge's step (c.1). Tests for their existence were removed.
 
   test("fails closed when merge-base is unresolved instead of falling back to git diff HEAD", async () => {
     const content = await readRepoFile("plugins/compound-engineering/skills/ce-code-review/SKILL.md")