feat(cli): expand skills get with --ref flag, include agents/ in --full, drop scripts from bundle

[christso]

Context

PR #1224 bundles skills into the npm package and adds agentv skills subcommand. This issue addresses follow-up refinements discussed in design review.

Changes

1. Add --ref flag to skills get

Allow loading individual reference files without --full:

agentv skills get agentv-bench --ref eval-yaml-spec    # one reference
agentv skills get agentv-bench --full                   # all references (existing)
agentv skills get agentv-bench                          # SKILL.md only (existing)

Implementation: read <skill-dir>/references/<ref>.md (or templates/<ref>) and print to stdout.

2. Include agents/ in --full output

Add agents to the readSkill collect loop so agent role definitions (executor.md, grader.md, etc.) are included when --full is used:

// Before
for (const sub of ['references', 'templates']) {
// After
for (const sub of ['references', 'templates', 'agents']) {

3. Drop scripts/ and assets/ from bundled skills

Scripts (Python, bash, HTML) should not be shipped in the skill bundle. Either:

• Convert to CLI subcommands (e.g. agentv eval lint replaces lint_eval.py)
• Or remove entirely if not needed (onboarding script already covered by agentv init, trajectory HTML by agentv studio)

Remove scripts/ and assets/ directories from apps/cli/skills/ before the build copies them to dist/skills/.

4. Update SKILL.md files to document skills path usage

Add a note to each skill's SKILL.md explaining how to access individual reference files:

## Accessing reference files
To load a specific reference, use:
bash
cat $(agentv skills path <skill-name>)/references/<filename>.md

Or use the --ref flag: agentv skills get <skill-name> --ref <filename>

5. Remove plugin requirement from docs

Update README and onboarding docs to reflect that npm install -g agentv is sufficient — no separate plugin installation needed.

Relationship to agent-browser

This aligns agentv with agent-browser's pattern: skills are bundled in the npm package at dist/skills/ (analogous to skill-data/), agents read files from the known path via skills path, and --full is a convenience shortcut for bulk loading.

Acceptance criteria

• skills get <name> --ref <file> returns a single reference file
• skills get <name> --full includes agents/ content
• scripts/ and assets/ removed from bundled skills
• SKILL.md files document skills path usage
• Plugin install no longer required (docs updated)
• Existing tests pass

Parent

#1224

[christso]

Additional change: move skills to repo root

Move apps/cli/skills/ → skills-data/ at the repo root (like agent-browser's skill-data/).

Steps:

1. Move apps/cli/skills/ → skills-data/ at repo root
2. Update apps/cli/tsup.config.ts to copy from ../../skills-data instead of skills:

   const srcSkillsDir = path.resolve('..', '..', 'skills-data');

3. Remove the old apps/cli/skills/ directory
4. Verify skills path still resolves correctly
5. Run tests to confirm nothing broke

Why:

Aligns with agent-browser's pattern where skill content lives at the repo root, not nested under an app. Skills become visible and accessible at the top level of the monorepo.

Parent:

#1229