Add dbt-agent-skills as git submodule

[tayloramurphy]

Summary

• Adds dbt-labs/dbt-agent-skills as a git submodule in vendor/dbt-agent-skills
• Symlinks 10 individual skills into skills/ so they're auto-discovered by the plugin system
• No changes to existing skills or plugin configuration

How it works

The submodule pins to a specific commit in the dbt-agent-skills repo. Symlinks in skills/ point through vendor/ so auto-discovery finds them at the expected skills/*/SKILL.md path.

vendor/dbt-agent-skills/          ← submodule (full repo)
skills/running-dbt-commands/      ← symlink → ../vendor/dbt-agent-skills/skills/dbt/skills/running-dbt-commands
skills/adding-dbt-unit-test/      ← symlink → ../vendor/dbt-agent-skills/skills/dbt/skills/adding-dbt-unit-test
...

Skills added

Skill	Source group
adding-dbt-unit-test	dbt
answering-natural-language-questions-with-dbt	dbt
building-dbt-semantic-layer	dbt
configuring-dbt-mcp-server	dbt
fetching-dbt-docs	dbt
running-dbt-commands	dbt
troubleshooting-dbt-job-errors	dbt
using-dbt-for-analytics-engineering	dbt
migrating-dbt-core-to-fusion	dbt-migration
migrating-dbt-project-across-platforms	dbt-migration

Things to evaluate

• Clone experience: new clones need git clone --recurse-submodules or git submodule update --init after clone
• CI/CD: pipelines need submodule checkout enabled
• Symlinks on Windows: works on macOS/Linux; Windows needs developer mode
• Update workflow: bumping the submodule to a newer commit is a manual cd vendor/dbt-agent-skills && git pull && cd ../.. && git add vendor/dbt-agent-skills && git commit

Test plan

• Verify skills/*/SKILL.md resolves through symlinks
• Test fresh clone with --recurse-submodules
• Test plugin install and verify dbt skills appear
• Verify existing skills are unaffected