v0.12.0

Changed

• Close sweep runs all gates before any suite (#129): lint and typecheck now run for every
  project in the sweep set before any project's suite executes. A failing gate short-circuits the
  sweep immediately — no suite runs, and next_action returns fix_regression with the failing
  gate entry. Previously each project ran its suite first and only then checked its gates.
• Adapter._gate stops at the first failing command (#129): the first non-zero exit ends the
  gate; subsequent commands in the same gate list are not executed.
• Gate memoisation (#129): a gate whose project tree hash is unchanged since it last passed
  within the same run is skipped (no command executed) and recorded with skipped = 1 in
  gate_result. A failed gate or a changed tree always re-runs.
• fix_regression detail wording (#129): the reply for a gate failure now reads
  "Close sweep stopped before the suite: lint/typecheck gates failed." (was "Close sweep is green but lint/typecheck gates failed.").
• Schema v11 (#129): gate_result gains tree_hash TEXT and
  skipped INTEGER NOT NULL DEFAULT 0. Existing ledgers are migrated on open via MIGRATIONS[10].