Selective skill installation missing `gws-shared` dependency + nonexistent `gws generate-skills` command

[serejke]

Problem

The README documents selective skill installation:

npx skills add https://github.com/googleworkspace/cli/tree/main/skills/gws-drive

This installs only gws-drive/SKILL.md, but the skill's PREREQUISITE line says:

Read ../gws-shared/SKILL.md for auth, global flags, and security rules. If missing, run gws generate-skills to create it.

Two issues:

1. gws-shared is not installed — the npx skills CLI doesn't resolve cross-skill references. An AI agent following this skill will lack authentication instructions, global flags, and security rules.

2. gws generate-skills doesn't exist — this command is referenced in every service-level skill's PREREQUISITE line, but there's no such subcommand in the CLI. It appears to be orphaned documentation.

Suggested fixes

Option A (skill-side): Add a depends field to each skill's frontmatter (requires upstream support in vercel-labs/skills — see vercel-labs/skills#860):

depends:
  - gws-shared

Option B (docs-side): Update the selective install docs to explicitly include gws-shared:

# Always install the shared skill first
npx skills add .../skills/gws-shared
npx skills add .../skills/gws-drive

Option C (CLI-side): Implement the gws generate-skills command referenced in the PREREQUISITE lines, or remove the reference if it's not planned.

[Bortlesboat]

Confirmed from the current README that the selective install docs still show npx skills add .../gws-drive / .../gws-gmail directly, with no gws-shared step, and I also can't find a gws generate-skills command in the CLI surface.

I think the least-surprising fix is docs-first:

1. remove the gws generate-skills hint from the PREREQUISITE lines
2. update the selective-install docs to always install gws-shared first
3. treat dependency metadata / auto-install as follow-up once the upstream skills tooling supports it

That gets agents onto a working auth/security path immediately without waiting on new installer behavior.

[Bortlesboat]

Opened #687 for this.

While wiring it up I found gws generate-skills is still the right instruction for local checkout generation; the selective-install breakage here was that the README and generated prerequisite text never told people to install gws-shared. The PR updates both paths so they point to the right fix for each case.