v0.1.5 - adding factory-db-migration skill & agent

Outcome: v0.1.5 — factory-db-migration skill + db-migration-engineer agent

Why: Codifies lessons from running first production DB migration. The skill is structured to have a pre-flight / seed / verify / rollback functionality. All of which should be able to run locally before ever touching production. The skill is structured for continuous update — new failure modes append as new sections.

Changes:

feat:

• factory-db-migration skill — 12 Principle/Why/Recipe/Failure-mode sections: data-as-ground-truth, three-stage write contract (preflight/mutate/verify/rollback), idempotency by natural key, bidirectional update semantics, validate-at-parse, layered backup independence (Layer C), human-gated execution, defense in depth, local→staging→prod testing protocol, migration PR shape
• db-migration-engineer agent — sister to db-schema-architect; owns the runbook, not the schema. Outputs runbook + gating criteria, not raw SQL. Refuses to auto-run any DB command
• factory-pitfalls — 11 new failure-mode entries under "Database migrations (destructive prod writes)"
• /prompt slash command — rewrite rough one-liners into structured XML-tagged form using the factory-prompting.md vocabulary
• /kit-audit slash command + measurement script — quantify the kit's token footprint, identify trim candidates

fix:

• .gitignore — stop tracking .claude/ (was leaking per-machine state)

Source provenance: synthesized from Kairos KAI-138 historical-orders seed cycle and KAI-126 backup doctrine work. The skill is project-agnostic but every principle has a concrete Kairos failure mode it was hardened against.