fix: docs is_active column and selectWorkingDiff sql syntax

[caffeinum]

Summary

Fixes two bugs discovered when following the getting-started guide:

1. Documentation bug: The getting-started.md example used .where("is_active", "=", true) on the version table, but this column doesn't exist. The active version is tracked in a separate active_version table. Fixed by using proper join with active_version table.

2. selectWorkingDiff SQL syntax error: The function was incorrectly embedding Kysely query builders into a raw SQL template string, causing "near 'from': syntax error". Fixed by using Kysely's native .unionAll() method instead.

Changes

• packages/website/content/docs/getting-started.md: Updated active version query to use active_version table join
• packages/sdk/src/diff/select-working-diff.ts: Replaced raw SQL union template with Kysely's .unionAll() method

Testing

• All 9 select-working-diff.test.ts tests pass
• All 11 diff module tests pass