Install script does not create next-steps-after-plan.md data file

[williamthorsen]

Problem

The install command skips all _-prefixed directories under content/skills/, which prevents _data/ (shared reference data) from being deployed. 20+ skills reference _data/ files via relative paths — when these files are missing, skills lose context or fall back to hardcoded defaults.

Context

The _-prefix filter was introduced to exclude both _data/ and _platforms/ from the main install loop. _platforms/ genuinely needs separate handling (platform-specific skill routing), but _data/ should be installed as a regular sibling directory alongside skills.

The _data/ directory contains 9 reference files: artifact-conventions.md, branch-format.md, case-conventions.md, commit-format.md, git-commands.md, naming-conventions.md, next-steps-after-plan.md, next-steps-after-review.md, work-types.md.

Skills reference these via relative paths like _data/next-steps-after-plan.md or ../_data/commit-format.md.

Solution

Change the underscore-prefix filter in installSkills from entry.startsWith('_') to entry === '_platforms'. This installs _data/ through the existing installSkillEntry path (which handles copy, link, drift detection, and manifest tracking) while still excluding _platforms/ (which has its own dedicated installation logic).

Acceptance criteria

• _data/ directory is installed to ~/.claude/skills/_data/ and ~/.rovodev/skills/_data/
• Works in both copy and --link modes
• _data/ entries are tracked in the manifest (enabling drift detection and uninstall)
• _platforms/ directory is still excluded from the main install loop
• Existing tests updated to reflect the new behavior