- Bundle SKILL.md at src/dbread/assets/skill.md, shipped in wheel
- Auto-install to ~/.claude/skills/dbread/SKILL.md when running
  `dbread init` and ~/.claude is present (silent skip otherwise)
- New subcommand `dbread install-skill [--force]` for reinstalls after
  upgrade
- Skill teaches Claude: discover-before-query workflow, SQL vs Mongo
  routing, error recovery (guard / rate-limit / timeout), PII hygiene
- Validated against official Agent Skills spec: name max 64 chars +
  directory match, description third-person, body < 500 lines

CI fix (retention test):
- test_retention_opportunistic_throttles_per_hour was platform-dependent
  (time.monotonic() origin differs Linux vs Windows); use a relative
  offset so it passes on both.

Tests: 289 total (+9 skill tests), ruff clean.