feat(laddr-import): row → v1 translators with slug + stage + tag normalization

Per-table translator functions that map a raw laddr row into a v1
record (Zod-shape, not yet validated). Mints UUIDv7s, threads them
through cross-table id maps for FK resolution, and emits warnings for
soft-fixed conditions (invalid slugs, unknown stages, dropped context
classes).

Normalization rules pulled from data-model.md:
  - slugs slugified + dedupe-with-suffix when source doesn't match the
    new regex (default per plan; document in Notes)
  - stage TitleCase → lowercase, unknowns fall back to "commenting"
  - tag handles like "topic.transit" split into namespace + slug
  - ContextClass "...Project" / "...Person" → taggableType
  - Email + password hash routed to PrivateProfile +
    LegacyPasswordCredential separately (never in the public side)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: themightychris