docs(migration): note that t.timestamps() also adds deletedAt (#2313)

[bpamiri]

Summary

• Three v3-0-0 doc spots described t.timestamps() as creating only createdAt and updatedAt. The implementation in vendor/wheels/migrator/TableDefinition.cfc:372 actually adds three columns; the third is deletedAt, the soft-delete marker.
• The v4-0-0-snapshot guide and the v3 database-migrations index already say "createdAt, updatedAt and deletedAt" — this PR aligns the remaining three v3 spots so the picture is consistent.
• Resolves the t.timestamps() line in Polish bucket: minor CLI / framework / doc inconsistencies surfaced by VM-onboarding journals #2313.

Why docs and not opt-in

The issue explicitly recommends the docs path:

Make the soft-delete column opt-in (t.timestamps(softDelete=true)), or update the docs to accurately describe the three-column behavior. (Note: the project's own CLAUDE.md anti-pattern #7 already documents the three-column behavior, so the docs side may be the right move.)

Making the soft-delete column opt-in would silently change the migration output for every existing Wheels app on disk — a backward-compat break for cosmetic gain. Documenting the existing behavior is the right move.

Files changed

File	Before	After
using-sqlite.md	// Creates createdAt and updatedAt as TEXT	// Creates createdAt, updatedAt, and deletedAt as TEXT
cli-guides/migrations.md	// Creates createdAt and updatedAt	// Creates createdAt, updatedAt, and deletedAt (soft-delete marker)
commands/generate/migration.md (table row)	Creates createdAt and updatedAt	Creates createdAt, updatedAt, and deletedAt (soft-delete marker)

Test plan

• No code paths touched — pure doc fix.
• Wording matches the existing accurate references in v4-0-0-snapshot/glossary.mdx and v4-0-0-snapshot/basics/migrations.mdx.