Merge step (c): converge to ce-* convention for agents and skills

Aligns local custom agents, skills, and modified shared agents with upstream's
flat ce-<name>.agent.md + ce-<skill>/ convention introduced in upstream v3.x.

Changes:
- Delete 9 upstream-renamed agents for locally-dropped agents (design/*, rails
  reviewers, ankane-readme-writer, data-migration-expert, performance-oracle,
  security-sentinel)
- Delete ce-dhh-rails-style skill (local dropped dhh-rails-style entirely)
- Move 5 custom agents to flat ce-<name>.agent.md paths:
  * python-package-readme-writer, design-conformance-reviewer,
    tiangolo-fastapi-reviewer, zip-agent-validator, lint
- Rename 12 custom skill directories with ce- prefix:
  * john-voice, jira-ticket-writer, hugo-blog-publisher, weekly-shipped,
    proof-push, ship-it, story-lens, sync-confluence, excalidraw-png-export,
    python-package-writer, fastapi-style, upstream-merge
- Port local Python/FastAPI edits into upstream's flat ce-best-practices-
  researcher.agent.md and ce-kieran-python-reviewer.agent.md
- Update frontmatter name: fields in all 17 renamed files to match new paths

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

plugins/compound-engineering/agents/ce-best-practices-researcher.agent.md

@@ -25,7 +25,7 @@ Before going online, check if curated knowledge already exists in skills:
 
 2. **Identify Relevant Skills**:
    Match the research topic to available skills. Common mappings:
-   - Rails/Ruby → `ce-dhh-rails-style`
+   - Python/FastAPI → `ce-fastapi-style`, `ce-python-package-writer`
    - Frontend/Design → `ce-frontend-design`, `swiss-design`
    - TypeScript/React → `react-best-practices`
    - AI/Agents → `ce-agent-native-architecture`
@@ -83,7 +83,7 @@ Only after checking skills AND verifying API availability, gather additional inf
 
 2. **Organize Discoveries**:
    - Organize into clear categories (e.g., "Must Have", "Recommended", "Optional")
-   - Clearly indicate source: "From skill: dhh-rails-style" vs "From official docs" vs "Community consensus"
+   - Clearly indicate source: "From skill: ce-fastapi-style" vs "From official docs" vs "Community consensus"
    - Provide specific examples from real projects when possible
    - Explain the reasoning behind each best practice
    - Highlight any technology-specific or domain-specific considerations
@@ -106,7 +106,7 @@ For GitHub issue best practices specifically, you will research:
 ## Source Attribution
 
 Always cite your sources and indicate the authority level:
-- **Skill-based**: "The dhh-rails-style skill recommends..." (highest authority - curated)
+- **Skill-based**: "The ce-fastapi-style skill recommends..." (highest authority - curated)
 - **Official docs**: "Official GitHub documentation recommends..."
 - **Community**: "Many successful projects tend to..."