v0.2.1

Documentation and tooling. No library code changed.

Added

• README section comparing Scriba with Commanded.Event.Handler — the
  alternative that actually ships with Commanded, and the one a reader is
  most likely weighing Scriba against. It says what the handler gives you
  (:concurrency, partition_by/2, handle_batch/1, error/3), the two
  constraints worth knowing (batching and concurrency cannot be combined;
  acknowledgement happens when handle/2 returns, so the read-model
  database holds no record of progress), what Scriba adds, and when the
  handler is the better choice.

  The README argued only against commanded_ecto_projections, whose last
  release was January 2024 — which meant the pitch never addressed the
  maintained option.

  Checked against Commanded 1.4.11, which is now also what the test suites
  run against (mix.lock moved 1.4.9 → 1.4.11, both suites green). The
  section names that version, because a comparison with no version on it goes
  stale silently — 1.4.10 added :batch_timeout, which the first draft of
  this section missed by reading a vendored copy.

• mix scriba.gate — the release gate from architecture §14 as a command
  that exits non-zero. Checks version consistency (the README install snippet
  against mix.exs, and scope claims pinned to older versions), that the
  CHANGELOG has an entry for the current version and nothing stranded under
  [Unreleased], then format, compile, credo, docs warnings, dialyzer, tests
  and hex.build.

  It exists because 0.2.0 shipped with {:scriba, "~> 0.1"} in its install
  snippet — the most-copied block in the README — after an audit that flagged
  it and a gate I reported as passing. A list a human interprets is not a
  gate.

Fixed

• Stale version references across the shipped documents: the README install
  snippet (~> 0.1 → ~> 0.2) and its "only source shipped in v0.1" note,
  five "no equivalent in v0.1" cells in MIGRATION.md, and five section
  headings and scope sentences in SCRIBA_ARCHITECTURE.md that pinned current
  behaviour to v0.1.

• examples/bank and mix bench.throughput did not truncate
  scriba_watermarks, so a stale watermark survived a reset.