feat(migrations): complete idempotent migrator CLI and Docker packaging

[WoLfulus]

Finish the migrations module so it is a working CLI that converges a
database to the Kysely migrations baked into a Docker image, and can build
that image.

Engine (databases.ts):

• Fix undefined compileModule -> modules.compile when persisting the
  compiled up/down script on each migration row.
• Fix dialect resolution indexing factory by raw url.protocol instead of
  the mapped dialect name (sqlite/postgres/mysql were never resolved).
• Bind SQLite executed timestamps as ISO strings; a Date object cannot be
  bound by the sqlite driver.
• create() accepts a string URL; build()/create()/dialect()/destroy()
  get explicit return types; unused/type-only kysely imports cleaned up.
• Fix inverted getFutureMigrations filter.

CLI (cli/*):

• Register subcommands on migrate: apply, status, list, rollback, build.
• apply idempotently converges: migrates up when the image is ahead, and rolls
  down (using the compiled down script stored in the database) when the image
  is behind; --no-rollback refuses instead. status/list/rollback added.
• Shared --database / --migrations-dir options with DATABASE / MIGRATIONS_DIR
  env fallbacks resolved in support.ts.
• build renders a two-stage Dockerfile (compile migrator, run apply on start)
  and invokes docker build; --dockerfile renders only.
• Remove dead migrator.ts; mod.ts re-exports the library API; add ./cli export.

Add README documenting the workflow.

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01PsF13E7YqG6oAshFoTdaUM