feat(jpa): implement the JPA relational persistence platform

Implements the Stable and Experimental JPA persistence platform designs
against real PostgreSQL, adapted to this repository's fail-closed 19-leaf
registry.

The design models the platform as 25 Gradle projects. `src/settings.gradle`
throws unless the registry holds exactly 19 leaves, so the plan's modules
become packages inside `:adapter:outbound:persistence-jpa` (starter in
`:app-bootstrap`, testkit in its own source set). The full mapping, the
renames this repository's naming gate required, and every deliberate
substitution are recorded in `docs/jpa/repository-adaptation.md`.

Seven Docker-backed lanes replace the plan's seven JVM test suites. Each
fails closed: a lane that discovers nothing, or a container that cannot
start, is an error rather than a skip.

Three defects the contracts found against a real server:

- `CommitFailureClassifier` treated only SQLSTATE 40003, class 08, and
  transport breaks as completion-unknown. A backend terminated mid-commit
  reports 57P01, and the commit record may already be in the WAL — so a
  possibly-committed transaction could be re-run. 57P01/57P02/57P03 now
  classify as completion-unknown.
- `SchemaTenantMigrationOrchestrator` recorded `MigrateResult`'s target
  version, which is empty for a tenant already current, reporting migrated
  tenants as unmigrated during a partial rollout. It now reads the applied
  version back from the tenant's schema history.
- `JpaStreamExecutor` checked only the declared return type for reactive
  publishers, and `RegisteredPostgreSqlCopyLoader` passed the COPY timeout
  to `SET`, which is parsed before parameter binding.

`JpaModuleBoundaryTest` enforces the plan's module map as package rules;
`verifyCleanArchitectureDependencies` governs edges between leaves and
cannot see these. Its first assertion is that the import is non-empty,
because every rule under it is a `noClasses()` rule and would pass
vacuously on an empty import.

Verified: 128 container tests across all seven lanes, 1183 unit tests,
`:adapter:outbound:persistence-jpa:check`, `:app-bootstrap:check`,
`verifyCleanArchitectureDependencies`, `verifyOneTypePerFile`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/jpa/experimental-promotion-checklist.md

@@ -0,0 +1,43 @@
+# Experimental Promotion Checklist
+
+`ExperimentalPromotionGate` evaluates this checklist. Every technical item, then the ADR.
+
+## Technical evidence
+
+- [ ] **Compatibility** — the Stable contract suite passes on the experimental target, twice, on two
+      supported patch releases. One passing run is a coincidence.
+- [ ] **Security** — for tenancy features, cross-tenant read *and* write are both proven impossible,
+      including through native SQL, bulk DML, `getReference`, and the second-level cache. A filter
+      that covers only entity queries covers none of those.
+- [ ] **Failure** — connection reuse does not leak tenant context; a failover does not silently route
+      a read-after-write to a stale replica; the commit-ambiguity scenarios still behave.
+- [ ] **Migration** — per-tenant migration is resumable after a partial failure, and rate-limited.
+      With one schema per tenant, a run is N independent migrations and "it failed" is not an answer.
+- [ ] **Performance** — pool capacity, replica lag under load, and per-tenant memory are measured,
+      not estimated. Database-per-tenant fails as a sum, not as an individual pool.
+
+## Decision
+
+- [ ] **Reviewed ADR** — recording what is being promised, the operational burden it carries, and
+      what would cause it to be withdrawn.
+
+The ADR is not a formality. The technical suites establish that something works; the ADR records
+that the platform should promise it, which is a different question with a different cost.
+
+## What does not count as evidence
+
+- The version being generally available.
+- The feature working in one environment.
+- A passing suite that skipped because Docker was unavailable.
+- A green lane whose assertions were relaxed to make it pass.
+
+## Outcomes
+
+| Decision | Meaning |
+|---|---|
+| `BLOCKED_TECHNICAL` | at least one suite has not passed |
+| `BLOCKED_MISSING_ADR` | evidence is complete; no reviewed decision exists |
+| `ELIGIBLE_FOR_STABLE_REVIEW` | both; Stable review may begin |
+
+The two blocked states are distinct because they need different work: one needs evidence, the other
+needs a decision.