v0.1.0:41 — second hotfix to migration 0009; migration regression tests

The v0.1.0:40 migration was correct on clean installs but crashed at
COMMIT on any database with rows in discount_redemptions: SQLite's
deferred FK check saw the dropped parent's bookkeeping as unsatisfied
even after the rename. Fix is to rebuild discount_redemptions in the
same transaction (stash → drop → rebuild → restore) plus orphan
cleanup. Migration is idempotent; operators on :40 with a checksum
mismatch recover by deleting the version=9 row from _sqlx_migrations
and restarting.

Lands the missing migration test scaffolding too. The four tests in
licensing-service/tests/migrations.rs apply migrations against a
realistic populated database (products, policies, invoices, licenses,
machines, discount codes, redemptions, webhooks, tip attempts). The
regression test fails with the exact 787 error against the v40
migration — would have caught the bug pre-release.

KEYSAT_INTEGRATION.md is removed from this repo; it now lives in the
parent licensing/ folder.

licensing-service/Cargo.toml

@@ -98,6 +98,11 @@ html-escape = "0.2"
 rust-embed = { version = "8", features = ["mime-guess"] }
 mime_guess = "2"
 
+[dev-dependencies]
+# Each integration test gets its own throwaway sqlite file. tempfile gives
+# us NamedTempFile so the OS cleans up if a test panics mid-run.
+tempfile = "3"
+
 [profile.release]
 opt-level = 3
 lto = "thin"