Add Codex/Gemini adapters, fix sync.sh and cross-adapter compatibility

[sebastientaggart]

Summary

• Add Codex and Gemini adapter configs and headers for multi-agent support
• Fix sync.sh to apply placeholder substitution to frontmatter descriptions (not just body)
• Fix sync.sh validation to check frontmatter for unresolved placeholders
• Add {{#if KEY}} conditional block support to sync.sh for mode-aware skill rendering
• Fix review/ship skills to fall back to inline review when sub-agent spawning is unavailable
• Fix setup skill Check 7 to detect any adapter output directory
• Fix Makefile: set INTEGRATION_BRANCH=dev, use variables for deploy targets, add make help
• Fix /version to pull before bumping (prevents stale-branch push failures)
• Fix /start to pull integration branch before creating feature branches
• Update .gitignore with standard patterns, remove tracked .DS_Store
• Add ROADMAP.md capturing future work (swarm mode, three-branch Makefile targets)

Issue #11

[sebastientaggart]

Review Summary

Verdict: APPROVE

Findings

• [NOTE] The PR description claims "Fix /start to pull integration branch before creating feature branches" but no corresponding change was found in skills/start.md, the generated output files, or Makefile.agents.mk. This fix appears to be missing from the PR or was included in a prior commit not in this diff.

• [NOTE] The apply_placeholders on frontmatter descriptions and find_unresolved validation on descriptions (sync.sh lines 262-270) are correctly implemented. Conditional blocks, placeholder substitution, and the new adapter output path logic (using /SKILL.md as output_extension to create directory-based output like .agents/skills/start/SKILL.md) all work correctly via Python's Path handling.

• [NOTE] The generated output for the Claude adapter's release.md was initially confusing in the diff because the old multi-mode (trunk/two-branch/three-branch) sections were removed and replaced by the conditional-block-rendered two-branch content. The final generated file at .claude/commands/release.md is complete and correct with all 7 steps present.

• [NOTE] The Makefile correctly sets INTEGRATION_BRANCH = dev (overriding the development default from Makefile.agents.mk), adds help as the default goal, and references $(PRODUCTION_BRANCH) for deploy-prod which resolves to main via Makefile.agents.mk.