Monotonic create timestamps, future-dated guard, codegen_on_up, hardened skill

[heryr]

Hardens miiigrate against hand-written migration file names and closes the type-drift gap, following a real incident where an agent bypassed migrate::create and forged a future-dated timestamp (…120000).

Changes

• Monotonic migrate::create — new files are stamped after the latest migration on disk, so a future-dated hand-written name can never make subsequent files sort before an applied migration. Warns when it has to skip ahead of the clock.
• Future-dated guard — migrate::status returns a new future_dated list; migrate::up logs a warning before applying such a file. 5-minute clock-skew tolerance.
• codegen_on_up — new config knob (default: enabled when types_out is set) that runs migrate::codegen after an up that applied at least one migration; migrate::up returns the written path as types_path. Codegen failures are logged and never fail the run.
• SKILL.md rewritten — triggers on any database/schema work and states the hard rules: always scaffold with migrate::create, one migration per logical change, never edit applied files, check types_path after up.
• Docs: functions, configuration, README, changelog.

Validation

cargo fmt --check, cargo clippy --all-targets -- -D warnings, cargo test (52 tests) all green.

[heryr]

Merged manually into main as adf9782 (squash) — the GitHub API kept reporting the pre-amend head SHA after a force-push, blocking gh pr merge and reopen. Content is identical to the CI-validated branch. Released in v0.1.3.