feat: `dbts open` — open Snowsight at the sandbox

[luiul]

Summary

dbts open opens the Snowsight database page for the sandbox in the browser. dbts open my_model jumps straight to the table page.

Why

Cheap navigation win. Currently a copy-paste-the-DB-name dance. Saves ~5–10s every time you want to eyeball something visually.

Sketch

• Build the URL from target.account + DB name (and schema/table when an arg is passed).
• webbrowser.open(url).
• dbts open → DB page.
• dbts open my_model → table page (resolve schema via dbt manifest if needed, else default to target.schema).
• --target staging|live|dev like other commands; default sandbox.

Where it'd live

• ~30–50 lines. Could live in src/dbts/open_cmd.py (avoid shadowing stdlib open).

Effort

Small — half a day.

Tier

Tier 1 — recommended (cheapest UX win on the list).