feat: skill follow-up suggestions + dbt build project shorthand

[anandgupta42]

Problem

1. After completing a dbt skill (e.g., /skill dbt-develop), users don't know what to do next — they close the session instead of continuing with related tasks like testing, documenting, or analyzing impact.

2. Running dbt build without --model fails instead of building the entire project, which is the most common dbt workflow.

Proposed Solution

1. Skill follow-up suggestions: After each skill completes, show contextual "What's Next?" suggestions pointing to related skills (e.g., after dbt-develop → suggest dbt-test, dbt-docs, dbt-analyze).

2. dbt build project shorthand: When dbt build is invoked without --model, build the entire project via unsafeBuildProjectImmediately() instead of erroring.