D6f delivery + pre-release cleanup. Highlights:

- Deprecated-replacement family promoted from WARNING to ERROR in
  the default profile (0.0% noisy-hit rate on a 200-file googleapis
  sample empirically validated before promotion).
- Per-rule disable / enable surface across pyproject (disabled_rules,
  enabled_rules, "off" severity sentinel) + CLI (--disable-rule /
  --enable-rule + env-var equivalents) + programmatic from_dict.
- 26/26 buf v1.69.0 BASIC parity in recommended; default extends
  with the deprecated-replacement family (5 rules) +
  options/field-behavior-consistent.
- Schema version bumps "0.5" -> "0.6" for two new
  LintRuntimeWarning.category Literal values
  (contradictory_disable_config, unknown_rule_id).
- Pre-release polish: PEP 561 typed (py.typed + Typing :: Typed
  classifier), MIT LICENSE, README scrub of internal milestone
  breadcrumbs, buf Acknowledgments section with nominative-fair-use
  trademark hygiene, CONTRIBUTING.md AI-workflow + buf-is-optional
  clarifiers.

See CHANGELOG.md for the full per-delivery history.